remove bindings codegen h/cpp files from .gitignore

These files don't exist in the tree, and the codegen doesn't create
them, so we shouldn't have them sitting around in .gitignore.
Remove libgreen support.
Make 'mach doc' not fail when components/servo/target doesn’t exist.
Fix 'mach browse-doc' to use the right target directory.
Update web-platform-tests.
auto merge of #4202 : zwarich/servo/remove-libgreen, r=larsbergstrom
auto merge of #4205 : servo/servo/wpt_20141202, r=jdm
Update skia submodule to get android build fix.
auto merge of #4203 : SimonSapin/servo/refactor-doc, r=Manishearth
Support for Separated Read Write
auto merge of #4210 : glennw/servo/skia-android-update, r=metajack
Implemeneted ModifyAttribute handler to update DOM elements.
auto merge of #4214 : jdm/servo/modifyattr, r=jdm

Rebased from #4197.
Disable debugging, set wikipedia page for demo.
auto merge of #4216 : glennw/servo/android-demo, r=larsbergstrom
Don't categorize HTMLInputElement as a TableCellFragment

Closes  #4196.
auto merge of #4213 : jdm/servo/sepreadwrite, r=jdm

Rebased from #4211.
auto merge of #4217 : cmr/servo/issue/4196, r=jdm

Closes  #4196.

r? @jdm
Cleanup Document::GetDoctype.
Cleanup Document::GetDocumentElement.