解析pbxproj文件，并返回相应结构。
文件已经支持全部解析，但处理后的结构只包含以下类型
- PBXBuildFile section
- PBXFileReference section
- PBXGroup section
- PBXProject section
> ./PBXProjParser -f /path/to/project.pbxproj -s filename
/path/to/project.pbxproj
filename has been found. Searching...
../relative/path/to/filename- PBXContainerItemProxy section
- BXFrameworksBuildPhase section
- PBXFileReference section
- PBXHeadersBuildPhase section
- PBXNativeTarget section
- PBXResourcesBuildPhase section
- PBXSourcesBuildPhase section
- PBXTargetDependency section
- XCBuildConfiguration section
- XCConfigurationList section