added some examples for the Accept-Encoding header
moved accept header parsing to a slightly better place
detect whether gzip is an accepted and preferred content encoding
Added a test for anorm
changed things as requested by pull request review
[#826] Make Promise.{flat,}map allow supertypes
Merge pull request #1989 from asflierl/1983_correctly_handle_accept_encoding_gzip

correctly handle accept encoding gzip
Merge pull request #1992 from jroper/anorm-tests

Added a test for anorm
Merge pull request #1998 from baloo/improvements/826-Promise.flatMap

[#826] Make Promise.{flat,}map allow supertypes
Merge pull request #1995 from dylex/scalariformdoc

Add note about scalariform to contributor guidelines
Add ActionFunction, a generic version of ActionBuilder

Also includes some other useful refinements on ActionFunction: ActionRefiner,
ActionTransformer, and ActionFilter.  Proposal for issue #1986.
Update action composition documentation to describe ActionFunctiono

This replaces the previous section on different request types which manually
implemented ActionBuilders with roughly equivalent uses of ActionFunction.

Also reduced some headers to more clearly delineate the two sections (on
Actions and Builders).