Added support for OSX

* Minimum SDK versions required to build are iOSX 5.0 and OSX 10.7
* Full support for 7.28.1 (potentially fixes #5 -- thanks to @akikoskinen)
* Script now builds "packages" -- ios dev, ios distribution, osx dev/dist
* Updated README
Support for x86_64 on OSX

* Dropped i386 support on OSX (this is script requires OSX 10.7+ so it was kind of pointless...)
Add simulator support by default
Cosmetic (switch ' for ")
Cosmetic
Don't override source if folder exists

* Bump SDK version to 6.1
* Minor improvements on logging
Updated to build curl 7.29.0
Add support to build with debug symbols