Version 0.2A released.
- Moved the optional argument parsing function to the bare physics3.sty
- Added `*smallmatrix` supprot for the `xmat` module.
- Added the `\erfc` math operator in the `operator` module.
- Allowed users to select the `.tfm` blackboard font for the `\identity` and `\Identity` commands.
- Delivered the `bm-um` module to the `bm` package.
- Coding style uniformed; and updated the typeset of the doc.