- Added a number of headers to the umbrella header or XCode 6.1 will warn about missing headers.
- Fixed a typo that would prevent compilation.
Remove warning when compiled w/assertions blocked

This is just #351 as a PR. Not to steal @rodmaz's thunder or anything, but it'd be great to get this warning cleaned up upstream and eventually into our podfile!

From #351: `When CocoaLumberjack is compiled with assertions blocked (RELEASE), a warning is generated by the system on DDASLLogger.m (line 92) as the variable l is never used.`

Thanks!
Merge pull request #369 from augard/master

Fixed typo in LOG_LEVEL_ERROR definition
Merge pull request #367 from mike-lischke/master

Some small improvements + a compile fix
Fix imports
Merge pull request #368 from gempesaw/patch-1

Remove warning when compiled w/assertions blocked
Merge pull request #370 from rivera-ernesto/fix_imports

Fix imports
Bump beta version
Update DDLogLevel and DDLogFlag usage
Merge pull request #372 from rivera-ernesto/update_usage

Update DDLogLevel and DDLogFlag usage
Fixed warning from Xcode 6.1