Move ws_statement type into new file
Add function for initializing a statement
Add internal helper for appending and reallocating arguments
Add function for appending a direct argument
Add function for appending an indirect argument
Merge pull request #289 from neithernut/add-statement-assembly

Add statement assembly functions
Add deserializer callback interface
Add deserializer callback source file (stubs) and CMakeLists.txt entry
Add implementation for NULL callback
Add implementation for boolean callback
Add implementation for integer callback
Add implementation for string callback
Add implementation for start_map callback
Fix: Name of a command must be assignable.
Add implementation of map_key callback
Add implementation of end_map callback
Add implementation of start_array callback
Add implementation of end_array callback
We do not set the number callback

We don't set it because yajl uses the integer/double callbacks if we do
not set it, and these are preferable.
Add key for stack position argument type