`develop` has been deprecated in [this commit][1], `install` will
automatically use development mode.

[1]: 48ed586b

In version 0.12.8, attempting to use an uppercase 'F' to designate build format yields the error: 

[NoSuchOption]
 The "-F" options does not exist.
 build [-f|--format FORMAT]

Switching to lowercase 'f' to match the CLI's current configuration.

When loading installed packages pip freeze can output lines with
``===``, arbitrary equals, qualifiers instead of ``==``. This allows
poetry to parse either.

This fixes #433, based on the suggestion present in the discussion.