RFR: Updated section on Code Conventions.

[Andreas Lundblad]

Pull request for adding code conventions.

The code conventions in this pull request is a verbatim copy of [3]. These conventions were the ones discussed in
detail on discuss at openjdk.java.net in 2015. Two rounds of reviews were performed, [1] [2], and all comments were
addressed. The 6th and last draft [3] has been stable since then, and been in use by several OpenJDK projects.

[1] http://mail.openjdk.java.net/pipermail/discuss/2015-August/003766.html
[2] http://mail.openjdk.java.net/pipermail/discuss/2015-August/003771.html
[3] http://cr.openjdk.java.net/~alundblad/styleguide/index-v6.html

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Commit messages:
 - Removed all html from style guide.
 - Put Java specific sections in separate file.
 - Updated section on Code Conventions.

Changes: https://git.openjdk.java.net/guide/pull/14/files
 Webrev: https://webrevs.openjdk.java.net/guide/14/webrev.00
  Stats: 1495 lines in 3 files changed: 1493 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/guide/pull/14.diff
  Fetch: git fetch https://git.openjdk.java.net/guide pull/14/head:pull/14

PR: https://git.openjdk.java.net/guide/pull/14