Fixed present to not overwrite the previously added contents of the response body whebn called more than once.
Update to README documentation for issue #798

Refers to the use of /api/ at the beginning of sample routes to match
the use of 'prefix :api' in sample code.
Remove .format suffixes from paths if you narrow your API to only one format.
#809: update docs & changelog
Merge pull request #809 from ajvondrak/master

Don't use `.format` suffix in paths if you only have one format
fix include_missing for nested hash
Add declared description
add include_missing description
update changelog
Added missing method all_or_none_of for the parameters DSL.
Merge pull request #816 from georgimitev/fix_nested_hash_include_missing

fix include_missing for nested hash
Allow both desc and description in the parameter DSL.
custom validators should inherit from Grape::Validations::Base
Merge pull request #822 from rebelact/fix_readme_validator

Custom validators should inherit from Grape::Validations::Base
fix passing string value when hash is expected
Merge pull request #821 from rebelact/fix_hash_parameters

fix passing string value when hash is expected
Validate array params against list of acceptable values.
Routing methods dsl refactored to get rid of explicit paths parameter
Fixes #791
Specs for Mutually Exclusive and Exactly one of in groups

This adds tests for the `mutually_exclusive` and `exactly_one_of`
behaviour in a param group. References #699.
Documented how to use custom middleware, including ActionDispatch::RemoteIp refs: #648.