Added .proto parsing and convertion to .fbs.

Bug: 15777858
Change-Id: Iabef9b8c8044e593bb89510feebdee00d2f1840b
Tested: on Linux and Windows.
Added fenced code blocks to the C++/Java/Go docs for syntax highlighting.

Change-Id: I504915c6b5367e8c05dc056463158b8420ad8c5e
Tested: on Linux.