Translate version specifiers

[analog-cbarber]

Version specifiers in dependencies are simply copied from
the wheel without modification. This works for many cases,
but since the version comparison operators for pip and conda
are slightly different, some version specifiers will not work
properly in conda. Specifically,

• the compatible release operator ~= is not supported by conda.
  To translate, use a double expression with >= and *, e.g.:
  ~= 1.2.3 would become >=1.2.3,1.2.* in conda. This form is
  also supported by pip, so this is a viable workaround for packages
  you control.

• the arbitrary equality clause === is not supported by conda.
  I do not believe there is an equivalent to this in conda, but
  this clause is also heavily discouraged in dependencies and
  might not even match the corresponding conda package.

(There are other operations supported by conda but not pip, but
the are not a concern when translating from pip specifiers.)

As a workaround, users can switch to compatible specifier syntax when
possible and otherwise can remove the offending package and add it
back with compatible specifier syntax, e.g.:

whl2conda mywheel-1.2.3-py3-none-any.whl -D foo -A 'foo >=1.2.3,1.2.*'