Merge branch 'release/0.8'
Set version number to 0.9 dev.
Update release instructions.
Do not run cssutils filter in debug mode.

This was added in 72122af96f9456a9dca0ddbb3adaea2306454a38 without further
comment, but it doesn't make sense to me anymore. It's a compressor, it
should be production-only.
Added json:{path} to the list of valid manifest values.
Fix logic in css compilers doc
Jinja2 filter should run in debug mode
Update Stylus filter with include paths

Since the Stylus filter works with stdin, the compiler doesn't know the
source directory, and thus can't resolve any imports. This adds the
source directory to the include path using the `--include` option, and
also adds the `STYLUS_EXTRA_PATHS` option to configure any extra
include paths.
Merge pull request #203 from natefaubion/patch-1

Update Stylus filter with include paths
Make jinja2 run as an import filter
Merge pull request #205 from tgecho/feature/jinja-input-filter

Added ability to specify jinja as an input filter
Support referencing existing bundles in YAMLLoader.
Merge branch 'master' of git:webassets
Fix urls() output to correctly show url prefix
Fix small typo
Added filter for Closure's Soy Templates
Added Michael Su to AUTHORS
Change url() to urls() in docs
Merge branch 'master' of https://github.com/Emsu/webassets
Add __nonzero__ method to BaseEnvironment