Support for `--cflags` style option parameters, unit test, fixes #174

Based on the discussion already in #174, I removed the extra validation in required options so that they could handle cflag style option parameters. I also modified the `normalize()` function so that no additional normalization is performed on arguments following a require option. This accounts for a case like this:

```
COMMAND --cflags "-DDEBUG" 
```

without adjusting the normalization code, that would be normalized to:

```
COMMAND --cflags -D -D -E -B -U -G
```

but with the changes in this pull request it is handled appropriately.

All unit tests, included the one I added for this particular scenario, pass.