Port selector matching to use atoms.

Removed the Lowercase new type. This does mean that this
code path is slightly slower for now. This is because
find_equiv() doesn't work with atoms in hash tables, due to
the hash value being different than that of a string. However
it also means the removal of some unsafe code, and a better
long term solution will be to precache the lower case versions
as atoms.
Make Attr::owner immutable.

Nobody needs to change the element it's associated with, so there's no reason
to use a Cell here.
Fix rustdoc comment syntax
Get rid of fontconfig warnings for linux travis runs.
Merge pull request #3049 from glennw/fc-warnings

Get rid of fontconfig warnings for linux travis runs.
Merge pull request #3047 from mbrubeck/doc-comment

Fix rustdoc comment syntax
Merge pull request #3031 from Ms2ger/attr-cell

Make Attr::owner immutable; r=jdm
Fix the NodeFlags methods that are called by layout.

They should never borrow.
Add TreeWalker blob.
Add DOM Range blob.
Add DOM NodeIterator blob (include DOM NodeFilter interface).
Merge pull request #2987 from saneyuki/idl

Add some blobs for DOM Bindings
Prefer *Derived helper functions (is_*element) than string comparison
Merge pull request #3053 from brunoabinader/use-is-element-helpers

Prefer *Derived helper functions (is_*element) than string comparison
Fix doc.servo.org repository URL.
Unify the android + linux font code folders. Fixes #3028.
Merge pull request #3055 from glennw/unify-freetype

Unify the android + linux font code folders. Fixes #3028.
Correct the fallibility of proxy operations in the *Methods trait (fixes #3041).

A typo caused us to use the fallibility of the last normal method in the
interface.
Parallelize test runs on Travis (fixes #2980).
Merge pull request #3051 from metajack/fix-nodeflags-for-layout

Fix the NodeFlags methods that are called by layout.