Dynamic Library Install Name Base set to @rpath

It should be set for the app Frameworks directory and not the system /Frameworks
Set skip install for OS X framework
Merge pull request #357 from augard/master

Dynamic Library Install Name Base set to @rpath
- 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!
Fixed typo in LOG_LEVEL_ERROR definition
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
include QuartzCore/QuartzCore.h to propper support CGFloat
Merge pull request #373 from jonasschnelli/iOS8

include QuartzCore/QuartzCore.h to propper support CGFloat
Merge pull request #365 from CalQL8ed-K-OS/issue/347-Crash_on_iOS_7_in_DDASLLogCapture

DDASLLogCapture fixed for Xcode 6 running on iOS7 simulator in OS X Yosemite
fixed runtime crash on iOS 7.1 device, possible fixed for OS X 10.9

* using `MIN_REQUIRED` postfixed macros instead of `DEPLOYMENT_TARGET` postfixed ones
* tweaked the preprocessor conditional to test against iOS 8 instead of 7 to avoid runtime dynamic library linker crash
* refactored preprocessor code to be more readable and maintainable
Merge branch 'issue/347-Crash_on_iOS_7_in_DDASLLogCapture'

* issue/347-Crash_on_iOS_7_in_DDASLLogCapture:
  fixed runtime crash on iOS 7.1 device, possible fixed for OS X 10.9