Added new `requires` parameter to `Option`, arguments can now be
accessed from modes
Fixed bug which disabled `--` when using `Modes()` as options interface
Fixed bug when `requires` param wouldn't work when using `Modes()`,
improved algorithm in `Parser()._checkrequires()`,
new code in `Modes().type()`,
improved algorithm in `Modes()._modeindex()`
Update to 0.5.6: fixed bug in `_checkrequires()`
Update to 0.6.0: new `needs` parameter added to `Option()`,
parameters explained in docstring for `Option()`
Fixed bug in `_checkneeds()`: would raise an exception if no options
passed
Fixed bug in `_checkrequires()`: would raise an exception if one or more of the
options had no alias
Small changes in simple.py to reflect changes in CLAP