Add serialization for SeeC-Clang's parameter-decl mapping information.
Move getMappedValueFromMD() into its own file, as it will be used by the param
mapping.
Add MappedParam to represent SeeC-Clang mapping from parameter to llvm::Value.

Load MappedParam from the SeeC-Clang parameter mapping information, and store
them on the MappedFunctionDecl for the function that they belong to.
Merge updated upstream.