Use add... methods instead of get().add
Test for AnonymousExecutable.
unifies hashcode and equals of CtElementImpl
Add a test for createReference(String signature).
modifies OutputType enum..removes string field because values are producible without that field; fixes #81
Adding asserts.
Merge pull request #66 from seintur/unmodifiable_collection_bug
fixes ExecutableFactory and ExecutableFactoryTest for merging
refactors the code related to generic types

Before, there was three places for storing actual generic types (as opposed to declaration of generic type parameters):
in CtInvocation, in CtExecutableReference (setParameterTypes), in CtGenericReference.

Now, everything has been unified in a single place: CtGenericReference.
This facilitates much writing analysis and transformation of generics.

All tests pass after the refactoring.
Merge pull request #86 from monperrus/refactoring-generics
Merge pull request #76 from monperrus/hashcode
fixes a bug on the signature of null literals

If an expression has an empty signature, an exception is thrown in CtElement.equals.
This is the case for null literals.
The solution is to improve the signature of null literals.
feat #63 Refactors ImportScanner to get imports for a class

Create a new class for the old inner class ImportScanner,
CtImportScanner, and his new interface, CtImport, to have a
contract to retrieve all imports for a CtSimpleType element
(represent a class, an interface or an annotation). And
add a new test case to check if we are all useful imports.
Remove unused classes.
Remove unused imports.
Improve type checking.
Add some @SuppressWarnings annotations.
Merge pull request #90 from monperrus/bug-equal-signature-null
Merge pull request #78 from GerardPaligot/feat_63
Merge pull request #85 from boeserwolf91/output_type
Merge pull request #92 from seintur/code_cleanup
fixes a compilation bug with Java 1.6 (getDeclarationType twice defined)