This pull request includes two implementation: C extension and PHP
package. Both implementations support encode/decode of singular,
repeated and map fields.
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
