Restructuring protobuf to multiple modules

protobuf/java will become a parent pom that will contain two modules:

core - contains all of the code for the protobuf-java artifact
util - contains all of the code for the protobuf-java-util artifact

Also cleaned up various Maven warnings.

Prohibit null values in maps

Allow conformance test runner to tolerate crashes, and re-enable conformance tests

Fix typos in README.md/CHANGES.txt

Release the semaphore in dealloc, fixing leak.

Add the docs claimed define for HAVE_UNORDERED_MAP

On deserialization, missing values for message types
are replaced with a "default" message.

Fix appveyor build.

Ensure all formatted well-known-type values are valid JSON

Remove unused method in FieldCodec.

Improve number handling in JSON parsing

Update README.md - remove typo

Update README.md and remove INSTALL.txt

Remove the stale reference to test no longer around, and keep the performance test limited to just performance tests.

Remove the stale reference to test no longer around, and keep the performance test limited to just performance tests.

Added instructions on what tools to install to compile protobuf from
source. Removed the INSTALL.txt file because it's just a simple copy of
the autoconf documentation and confuses users.

Change-Id: I6fd8aa13495f1238fe5c62451b95ad480b1c4bed

Defer calls to mutable_unknown_fields() until it is actually required to
save memory for C++ lite runtime.

Change-Id: Ica9c1fd276cdb164942d1e7b6e098c83ee3ffdc5

Update version number and fix javadoc errors.

Fix up the conformance tests

This involves quoting timestamp/duration/field-mask values, even when they're not in fields.
It's better for consistency.

Fixes issue #1097.

- Tighten up on Infinity/NaN handling in terms of whitespace handling (and test casing)
- Validate that values are genuinely integers when they've been parsed from a JSON number (ignoring the fact that 1.0000000000000000001 == 1 as a double...)
- Allow exponents and decimal points in string representations

- Update all the new runner cases to handle a skip result as a skip and not a failure.
- Make ObjC use the new serialize_error result if it fails to generate the data.

Update objectivec/google/protobuf/Type.pbobjc.m

commit e841bac4 seems to have updated the
generated .pbobjc.h but not the .pbobjc.m to match.

Fix conformance test to only report skips in verbose mode.

commit e841bac4 seems to have mis-merged the
change to reporting skipped tests.

I didn't check if there were other merge issues.

Have the tests rely on the autocreator behaviors.