update(guidelines): updates developer guidelines and READMEs

added pull request and build improvements.
updated links
relative links
typo
update BUILD links
Update BUILD.md
Update CONTRIBUTING.md
Update CONTRIBUTING.md
Update CODING.md
Update CODING.md
Update CODING.md
Update CODING.md
Update CODING.md
Update CODING.md
Typo fix in README
Update CONTRIBUTING.md

Clarified that we're not yet ready for unsolicited submissions.
Update CONTRIBUTING.md

Removed docs section. Not applicable to Angular Material as written.
Update CONTRIBUTING.md

URL fixes for jsfiddle and plunkr
Update CONTRIBUTING.md

missed a paren in the last change
Update CONTRIBUTING.md

Removed confusing top-level menu items to other pages. Would rather folks went to the Submitting section.