CL: Add mbuf_append_and_free() and mbuf_move()

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It can specify how much data was actually processed and the rest will be re-delivered on next poll.

CL: mg: Add ability for multipart data handler to provide pushback

PUBLISHED_FROM=e0168c5064c3a32921c9209bc09f4da2079cd616

Replacement for fw_meta.py commands and also supports unbundling .hex files.

General syntax is:

```
 $ mos create-fw-bundle -o fw.zip part1:prop1=val1,prop2=val2,... part2:...
```

Example of building a mos fw bundle for ESP8266:
```
 $ mos create-fw-bundle -o fw.zip --platform esp8266 --build-info=build_info.json \
    boot:addr=0x0,src=rboot.bin,update=false \
    boot_cfg:addr=0x7000,size=0x1000,fill=0xff \
    fw:addr=0x100000,src=demo-c.bin \
    fs:src=fs.bin,type=fs,addr=0x8000,fs_size=262144,fs_block_size=4096,fs_page_size=256,fs_erase_size=4096
```

Example of converting a HEX file to a bundle:
```
 $ mos create-fw-bundle -o fw.zip host:type=host,src=hostfw.hex
```

CL: mos: Add create-fw-bundle command

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CL: none

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CL: mg: Read all available data during recv poll

PUBLISHED_FROM=b081025b9fb392c988924c7097b5333c38053f6f

CL: Add MG_MK_STR_N() and mg_str_starts_with()

PUBLISHED_FROM=f01003efc6aa6ff45fa99c7ad6e5319f5002f22d

Should use length of the exected response, not the response sent by the user.

CL: mg: Fix digest auth result comparison

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CL: none

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CL: none

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CL: Update mbedTLS to 2.13.1

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CL: mg: Check HTTP chunk size, ensure it's reasonable

PUBLISHED_FROM=d9f6babd314c092b42ce9e7fe31d6b30a38366a2

Clean the HTTP connection state when ia request/response has been fully
buffered and handler invoked.

Fixes https://github.com/cesanta/mongoose/issues/971

CL: mg: Fix handling of keepalive HTTP requests/responses

PUBLISHED_FROM=70c854aa306aacb9161f6ee48841f38dc0312e6b

Go back to Ubuntu 16.04 and older gcc-arm (4.9.3).

Boot loader just won't run when compiled with newer GCC (7.x).
It's likely that it can be fixed with compile switches but I couldn't figure it out quickly, so going to just downgrade for now to get it back to workign state.

CL: CC3200: Fix boot loader regression

PUBLISHED_FROM=b70b03bd17e03c7dae02328b32b855f3ca3ad6a9

CL: Add mgos_gpio_blink()

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PUBLISHED_FROM=694346bd6562c55e5ab00886df47f7cbfb0a3720

mbedTLS is just another lib now

CL: Use mbedTLS from mongoose-os-libs/mbedtls

PUBLISHED_FROM=bae4739d22e871bd268b8a3233dbb69634770243

CL: Integrate https://github.com/cesanta/mongoose/pull/667, fix documentation

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CL: none

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CL: Docs nits

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 * Update CubeL4 to 1.13.0
 * Rebuild OurTLS with `-DMBEDTLS_X509_CA_CHAIN_ON_DISK`
 * Add `-Wextra` and fix build issues

CL: Update STM32 build image

PUBLISHED_FROM=a7eacff7580bab6c6e40bdaf6164df575a717c55

Listeners still TODO

CL: ISM43XXX networking support (TCP, UDP client)

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CL: STM32: Make LWIP optional

PUBLISHED_FROM=eebffe7800a74d7b69aafd95e476b2e90328be98

Can be used for cases where device has no networking but mongoose is still needed for its event loop.

CL: mg: Add net_if_null, a no-op net interface

PUBLISHED_FROM=e79b4a8667508bbde1437dda9dad77ce3a3aa630

 * Change return type of mg_mgr_poll to return number of events
 * Add mg_mgr_min_timer
 * Refactor main poll loop to remove LwIP-specific stuff

CL: Refactor mg polling

PUBLISHED_FROM=dc94618b32fa3c84a2f053bd04d134297780ec82

CL: Fix https://github.com/cesanta/mongoose/issues/962 - file upload on windows

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A smattering of other related changes

CL: STM32 OTA support for L475-IOT01 and DISCO-F746

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CL: Mongoose 6.12

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h/t @M4GNV5

Fixes https://github.com/cesanta/mongoose/issues/943
Closes https://github.com/cesanta/mongoose/issues/944

CL: mg: Don't touch send_mbuf when sending MQTT messages

PUBLISHED_FROM=da7b4f8acec2e403caa4addd5739d036a6a74c76

Fixes https://nvd.nist.gov/vuln/detail/CVE-2018-10945

CL: mg: Fix body length calculation in mg_handle_cgi

PUBLISHED_FROM=0c30cf36fdb67c75f6148468701e23d6ee72d953

Closes https://github.com/cesanta/mongoose/pull/955

CL: mg: Add host name verification for OpenSSL

PUBLISHED_FROM=e35dd636ba7ce63116f0a38031074d22f6cd5dac

CL: Make esp8266 compilation a little less verbose

PUBLISHED_FROM=0ec1412ea32243f263d52fbe0877ecca1efc5aef

Closes https://github.com/cesanta/mongoose/pull/945

CL: Fix build with CS_ENABLE_STDIO=0

PUBLISHED_FROM=7d15f17fc42241facdba5b1004b5b7f3dda599dc

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CL: Add mg_strstrip: trims whitespace at the ends of s

PUBLISHED_FROM=a7e10054ac25fa2b3a878876da93a6b30d9507b3

Use vararg macros for this.

PUBLISHED_FROM=735c40b79dedef17a1fdbb5b846e984df0ae7018

h/t @YankunLi

Closes https://github.com/cesanta/mongoose/pull/939

CL: mg: Fix a bug in mg_mgr_init_opt with opts.num_ifaces

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