Added basic Expression classes

A lot of details, declarations and implementations are missing because
of unresolved discussions (statements vs. assignment expressions,
primitive operations vs. macros, etc.) as well as VariableIdentifier not
holding a ref to Value for function calls.
FunctionExpression Branch
Expression && LiteralExpression
Modified tests to remove FacadeExpression
Expression and LiteralExpression

- Moved FunctionInvocationExpression and pals to another branch, no
longer in this commit
- Changed some of the tests to use LiteralExpression
- Changed Value->TypeValue in TypeMismatchException
Formatting
Removed doc blocks
Reverted TypeMismatchException
add Namespace class, basic functionality, tests
re. #26
Merge branch 'namespace' of github.com:MurphEngineer/whdl into namespace

Conflicts:
	build.gradle
Merge pull request #39 from maxqchen/master

Added basic Expression classes
Merge branch 'master' of file:///home/mtrberzi/whdl/public into namespace
Added convenience NamespaceIdentifier constructor
Merge pull request #46 from lucaswoj/namespace-string

Added convenience NamespaceIdentifier constructor
add Namespace.containsIdentifier()
Merge branch 'master' of file:///home/mtrberzi/whdl/public into namespace
nit-picking of previous work, and test cases