[coding style] Migrate coding style guide from wiki
[coding style] Changes from review
Merge pull request #126 from crosswalk-project/coding-guidelines-1928

[coding style] Migrate coding style guide from wiki
[Android ext] Rewrite as simpler 'echo' example

As it's not possible to play audio files from file:// URIs in
versions of Crosswalk > 4 and < 8, replace the Android extensions
tutorial with a simpler "echo" tutorial.

This is also hopefully more useful to developers, as it contains
less code (generally) and should make it easier for them to
understand the parts of an extension and how they interact.
Merge pull request #127 from crosswalk-project/android-ext-rework-1962

[Android ext] Rewrite as simpler 'echo' example
[Android ext] Add note that Ant+Ivy are not required

While the extensions tutorial uses Ant+Ivy for the Java build,
these tools are not compulsory, and other tools could be used
as alternatives.
Update link to crosswalk-samples download
[Android] Update the javadoc of embedding API.

Some API changes in Crosswalk-7, so update the javadoc.

BUG=
Merge pull request #128 from sqliu/update-embedding-api-doc

[Android] Update the javadoc of embedding API.
Bump versions for Crosswalk 7 beta / Crosswalk 6 stable

NB downloads table now shows stable releases for Crosswalk webview
Update release notes links on Downloads page
[WebRTC] Add tutorial
[WebRTC] Add note about Crosswalk versions which support WebRTC