Implement Document.createComment.
auto merge of #1036 : Ms2ger/servo/createComment, r=jdm
implement NodeList and consolidate common scope and context retrieval
auto merge of #1018 : ttaubert/servo/nodelist, r=jdm

This should fix #652 and #775. I'm not sure if that's all that is needed to properly implement NodeList? Should we add tests somewhere? Sorry for any stupid stuff I might have done :)

r? @jdm
Fix eviction in MonoCache::find_or_create
configure: Prevent in-tree builds

Fixes #251.
Make rust-png depend on libpng

Fixes #1014.
Add CONTRIBUTING.md

Fixes #1026
Implement DocumentFragment.
Remove some type variables and an explicit dereference.
Implement Window::get_cx() to reduce code repetition.
Make Document::root private, in preparation for removing it as part of making Document a Node.
Fix parallel build with rust-auto-clean-trigger
Trigger Rust
Define "isnot()" for script test.
Pass AbstractNode to Node<ScriptView>.add_to_doc().
auto merge of #1054 : sanxiyn/servo/fix-stamp, r=jdm
auto merge of #1040 : kmcallister/servo/monocache, r=metajack
Basic Implementation of document.getElementById(), #740
auto merge of #1043 : kmcallister/servo/misc, r=larsbergstrom