Allow bundles to provide settings of their own.
Update Resolver API to receive context.
Write some comments for the resolver classes.
Move the resolver attribute to a proper config value.

This does not change the API, but makes it easier to set for bundles via the
existing constructor arguments.
Support bundle config settings in YAML loader.
ContextWrapper: Fix environment property, add get().
Fix some missing context wraps.
Update Jinja2 template tag for new syntax.
Make Filter class use context correctly.
Fix some comment grammar.
Script module had some issues with new API still.
Helpful exception when coffeescript is not installed
Support for utf-8 input files
Fix some tests that weren't passing perhaps due to utf-8

Or perhaps due to my node version. The coffe-script version
installed was the one from the requirements-dev
fix external filter on windows #156
Merge branch 'master' into feature/settings-tree

Conflicts:
	src/webassets/bundle.py
Merge remote-tracking branch 'origin/feature/settings-tree' into feature/settings-tree
Preserve exit status

Previously, webassets would always give exit status 1, which makes things that
use it think that it is failing.
Merge pull request #294 from asmeurer/exit0

Preserve exit status
Repaired missing os imports in various filters