adding function to get content of specific shim
0.4.5 allowing to access particular shim for extensibility
using include to properly include shims

- no more string modifications on the bundled string are necessary
- therefore shims don't have to be registered
- no dups are possible since browserify registers entries on hash
- removed all getters related to registered shims
- removed String.shim prototype override
- removed final shim call from all tests
adding tests to ensure shims get properly registered as prebundle files
updating readme and examples to improved api