raise instead of throw in validations spec
add ability to collect validation errors
Add missing quote in documentation
Merge pull request #432 from rymai/patch-1

Add missing quote in documentation
remove old line
add comment to explain if/else condition
Split long line
Stop testing Grape against unsupported Ruby 1.8.7 variants.
Merge branch 'master' of github.com:intridea/grape
update README.md
update CHANGELOG.md
do not add presence validators twice
remove backwards compatibility
Refactored a few API accessors.
Merge pull request #435 from namusyaka/refactor-some-codes

Refactored a few API accessors.
fixed curl calls to set the accept headers properly
Merge pull request #441 from CansaSCitySchuffle/fix-version-example

fixed curl calls to set the accept headers properly
API version can now take an array of versions.
specs for issue #319 (optional groups)
possible implementation for #319

Might be better to go with `optional_group(element)` than `group(element, required: false)`?