Currently, the generated header file might cause warnings if user specifies `-Wconversion` compiler option. This commit should be able to fix it.

* Update README.md

Fixed spelling error

* Update README.md

When browsing around the strutil files I found a function
that was never referenced inside the code base
"void StripString(string* s, const char* remove,
-                                 char replacewith);"

The name was kind of misleading as well and it seems like
it's a carbon copy of
"void ReplaceCharacters(string* s, const char* remove,
                                       char replacewith);"
(even the parameter names are the same, the code is the same..)

Is it intentional? Maybe for compatibility reasons? If so,
let's make it deprecated and use the ReplaceCharacters method inside
or the other way around.

Also, noticed there were no tests for "StripString" or "Replace".
Added some for both and planning on maybe making it more C++ish (?)
in another commit.

* Add document for php development

* Fix comments

Update Java Readme to 3.9.2

3.9.2 is on the Githib releases page.

The OSReadLittleInt64 function as defined by Apple reduces down to:

`return *(volatile uint64_t *)((uintptr_t)base + byteOffset);`

which means we are type-punning using a cast. On ARMv7 and other aligned architectures this can cause crashes. 
Minimal example: https://gist.github.com/dmaclach/b10b0a71ae614d304c067cb9bd264336

Fixes #6679 

The code in question hasn't change in a long time so the cause of
https://github.com/firebase/firebase-ios-sdk/issues/3851 still appears to be
an Xcode 11 clang change/bug; but this does appear to be slightly better
code for the work being done.

Cleanup along the way for #6679 

Fix incorrect Proto2 C# doc comments

* Cherry pick changes on update_version.py #6643

* Update version to 3.10.0-rc-0

* Do not add rc0 to php packages.xml

Simplify template exporting macros

* Down integrate to GitHub

* Remove unintentional double assign

* Change ByteCountInt64 to int64_t

* Revert changes in binary_conformance_test.cc

* Revert unnecessary changes

Remove duplicate entry in third party list

* Implement binary conformance test for oneof fields

* Update failure list

* Update failure list for php c extension

On the linked Wiki page, it can be seen that the creator is `opticron`, whose Github repository is also linked, and contains a more up-to-date implementation.

Linakge Monitor fix to handle a new version of protobuf-bom not available in Maven Central

* Sync upb

https://github.com/protocolbuffers/upb/pull/209

* Update upb

https://github.com/protocolbuffers/upb/pull/210

- use final instead of obvious types for local variables
- add missing `void` return type
- make the comments doccomments (///)

This adds links under the Clojure header to

https://protojure.github.ioSigned-off-by: Greg Haskins <gregory.haskins@gmail.com>

* Add binary conformance tests for map fields

* Update failure list

* Fix php conformance test

* Fix php conformance test

In 32-bit platform, int64 should be string. However, map iterator returns string key as integer.

* Add more test cases for map

* Update failure list

* introduce GOOGLE_PROTOBUF_SUPPORT_SYSTEM_MEMORY

* allow building net45 target on unix systems too

* add Span<> support on net45 as well

Document proto2 feature implementations in Google.Protobuf

C# Proto2 feature : Finale

Reworded info about message initialization

Addressed review comments

Java: Add Automatic-Module-Name entries to the Manifest