Change directory structure

Move implementation files in one directory to simplify podspec
Added "How to install" section to read me
Added nil check to global injector
Update pod spec to organize implementation files
Refactor

Separate protocols in BTKInjector into files
Update pod spec

previous conf does not pass lint.
Submodule cannot reference main module header file
Update import from BTKInjector
Release 1.0.3.