0.2.0

Changes:

• Add assignment methods (cadd_assign, csub_assign, etc.).
• Make second argument of ops traits use an associated type to improve type inference.
• Add more Cfrom implementations for converting byte array slices, OS strings, and paths to strings.
• Add type name to overflow error messages.
• Improve Cfrom error messages.
• Add code generator to improve ops module docs and fine-tune traits and functions.