Fake scanners out

- Use __halt_compiler(), and then define stub class, in order to trick
  classmap compilers into thinking a class exists.
Class stubs to force classmap generation
Allow finding class definitions following halt_compiler

- Allows finding class definitions following halt_compiler directives,
  effectively allowing polyfill support in classmap generation.
Added note in README about new polyfill support
Updated README to detail full change for polyfills
Trigger E_USER_DEPRECATED in deprecated polyfill autoload files