mega commit ! (will be broken up into smaller, documented + spec'ed commits later)
with support for:
- pbxProject.addProjectFile + support for .xcodeproj files in pbxFile :
adding sub-projects (importing .xcodeproj files)
- pbxProject.addToProjectBuildPhase :
adding sub-projects' targets to the main projects' build dependency section :
- pbxProject.addDependencyLibrary :
linking these sub-projects output (static libraries)
- pbxProject.copyBundleResource :
adding files to projects' build phase 'copy bundles'
- pbxProject.addToUserHeaderSearchPaths :
adding user header search paths
- pbxProject.addLinkerFlag :
adding linker flags (very wonky for now)

updated:
- addToheaderSearchPath to deal with recursive searches (just prepends '**' to the path)
changed pbxProject.addProjectFile() signature

now takes the pluginDir param and a path to the sub-project within that
directory rather than a fullPath for the sub-project