spare people the time deleting $ from text.

* Remove/replace travis references.

Add googletest as a submodule in third_party/googletest.

Fixes issue #1154 by noting that `vcpkg` contains protobuf. Potential improvements: also remark how to use `vcpkg` to get dependencies when building from source via CMake.

Added relative link to cmake guide.

Move the original README.md to src since it's talking about C++
exclusively and add a more general README.md to document how
to install protoc for all languages.

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

[ci skip]

Change-Id: I9391c09640e0b0b2b21c45a97a1fc91814d95c5d

Change-Id: Ic59d78d699af0e5f50377f83c8a7ea9a78074d81

Change-Id: I287d613fbe4180e41de67e26dfb905edeeebcf9d

in README.txt.

Patch (mostly) by Vincent Choinière <Choiniere.Vincent@hydro.qc.ca>.

committer: Jon Skeet <skeet@pobox.com>

- Improved readmes.
- Fixed incorrect definition of kint32min.
- Fixed absolute output paths on Windows.
- Added info to Java POM that will be required when we upload the
  package to a Maven repo.