Fix union header
Add method for initialisation of a ws_value_union from a value
Force enumeration value for invalid values to be 0
Merge pull request #243 from neithernut/add-values-union_features

Add union features
Add extensive documentation on stack semantics
Add processor stack type and files
Add interface and stubs to ws_processor_stack
Implement initialisation and deinitialisation function
Implement method for pushing on the stack
Implement method for poping from the stack
Implement method for accessing top and bottom
Add concept of frames
Add notes on frame semantics
Honor frame constrains when popping from the stack
Add convenience method for getting a value at a position
Move files for command processor
Extend processor interface and use new name for processor
Use new name in command headers
Fix type of special command function
Add initialisation and deinitialisation of the command processor