Only require the necessary bits of ActiveSupport

Addresses issue #353 -- Log formats silently changed between versions

The default log format changes after `require 'active_support/core_ext/logger'`, and
of course `require active_support/all` brings in everything including loggers.

To change the format back to the default for a particular logger, you can
use `my_logger = Logger::Formatter.new`.
Merge branch 'issue353-log-format-change' of github.com:rhunter/grape
Merged #354 and added a spec.
Fix: mount Grape middleware behind Error to allow error trapping, introduced in 48d05b50ec5351fdfde6a68b37d69c58a73c2381.
Fix: undefined method call for nil:NilClass for an API implementation without a block, now returs an empty string.
Preparing for 0.4.0 release.
Bump version to 0.4.1.
Update CHANGELOG.md
Update README.md, spec/request -> spec/requests
Merge pull request #372 from Radagaisus/patch-1

Update README.md, spec/request -> spec/requests
add protection