Implement minimal encoding support
#default_encoding should override reader encodings
We don't need to encode! preamable/postamble:

Ruby will do the conversion for us when we append.
Raise error on invalid encoding
Add some documentation about encodings
Detect BasicObject more accurately
Check for ::Erubis::Eruby in Erubis template

If the Erubis module had been defined but not the Eruby class (which
can happen if you require erubis/tiny) the Erubis template fails with an
"uninitialized constant" error.

Check for the specific Eruby class rather than just the containing
module in `engine_initialised?`
Update CHANGELOG
Doc tweaks
bump version
Travis: Remove rbx 1.8:

No-one has reported any issues so I'm just going to remove it from
Travis. Patches are still accepted, but I won't bother if no-one
actually uses it.
Make markdown test compatible with libxml2-2.9+.
Merge branch 'master' into minimal-encodings
Merge branch 'minimal-encodings'
Update CHANGELOG
Update version and gemspec
bump version
Refactor into Tilt::Mapping:

- Allow multiple mappings with Tilt::Mapping
- Replace global state with a Tilt::Mapping-instance
- Implement lazy loading (#160, #178)
- Remove initialize_template_engine and engine_initialized?
Add basic Mapping tests
Remove template engines from development dependency:

We're using Bundler for managing dependencies now.