Fix #170, rectify `argparse.r2py`

[aaaaalbert]

Also, add unit tests.

[aaaaalbert]

@yyzhuang, feel free to test this version of argparse for your project.

---

Unit test results from my humble machine:

albert$ for FILE in *_argparse_* ; do python utf.py -f $FILE ; done
Testing module: seattlelib
    Running: ut_seattlelib_argparse_scan_bool.r2py              [ PASS ]
Testing module: seattlelib
    Running: ut_seattlelib_argparse_scan_bool_default.r2py      [ PASS ]
Testing module: seattlelib
    Running: ut_seattlelib_argparse_scan_bool_missing.r2py      [ PASS ]
Testing module: seattlelib
    Running: ut_seattlelib_argparse_scan_int.r2py               [ PASS ]
Testing module: seattlelib
    Running: ut_seattlelib_argparse_scan_int_default.r2py       [ PASS ]
Testing module: seattlelib
    Running: ut_seattlelib_argparse_scan_int_missing.r2py       [ PASS ]
Testing module: seattlelib
    Running: ut_seattlelib_argparse_scan_int_missing_value.r2py [ PASS ]
Testing module: seattlelib
    Running: ut_seattlelib_argparse_scan_int_nonint.r2py        [ PASS ]
Testing module: seattlelib
    Running: ut_seattlelib_argparse_scan_int_uses_first.r2py    [ PASS ]
Testing module: seattlelib
    Running: ut_seattlelib_argparse_scan_str.r2py               [ PASS ]
Testing module: seattlelib
    Running: ut_seattlelib_argparse_scan_str_default.r2py       [ PASS ]
Testing module: seattlelib
    Running: ut_seattlelib_argparse_scan_str_missing.r2py       [ PASS ]
Testing module: seattlelib
    Running: ut_seattlelib_argparse_scan_str_missing_value.r2py [ PASS ]
Testing module: seattlelib
    Running: ut_seattlelib_argparse_scan_str_uses_first.r2py    [ PASS ]

[XuefengHuang]

I think we also need a unit test to check whether argparse_scan_str can parse non-str value of str argument, just like ut_seattlelib_argparse_scan_int_nonint.r2py

[aaaaalbert]

Hmmm, the point is that all callargs are strs in the first place (and are not parsed into str). Parsing from str is only done for int args.

Example: 123 is a string that can be parsed as an integer. xyz is a string that cannot be parsed as an integer. (Both are strings, still).

[XuefengHuang]

OK, that makes sense to me!