- Quantity as Generic class
- Add overloaded signature for __new__ Quantity
- Add typing module as private
- Add py.typed for PEP561 supports
- Add overloaded signature for __new__ Quantity
- Quantity as Generic class
- Add type hints throughout the project
- Add py.typed in package data in setup.cfg
- Add type hints for decorators
- Add type hints for public API of registry.py
- Add type hints for units.py

now the example runs correctly under doctests

commit 1b105987940a95891ad8223ded1e45a95621969d
Author: crusaderky <crusaderky@gmail.com>
Date:   Tue Jun 16 18:10:06 2020 +0100

    merge

commit d99b2407349f807f3f789be24b774c4ae0221dfa
Merge: e899082 583b297
Author: crusaderky <crusaderky@gmail.com>
Date:   Tue Jun 16 18:08:53 2020 +0100

    Merge remote-tracking branch 'upstream/master' into issue1112

commit e899082d4e504737d11c1562c41baaddfbc1fb8b
Merge: d3c65b6 af723fa
Author: crusaderky <crusaderky@gmail.com>
Date:   Tue Jun 16 09:36:04 2020 +0100

    Merge branch 'master' into issue1112

commit d3c65b62d225cbe344b877687ccc0e80c2c8af2c
Author: crusaderky <crusaderky@gmail.com>
Date:   Mon Jun 15 14:57:50 2020 +0100

    _active_ctx may contain empty maps

    commit d5df37560dd68a59fa42ced632a41debaaf6924b
    Author: crusaderky <crusaderky@gmail.com>
    Date:   Mon Jun 15 14:57:33 2020 +0100

        Fix

    commit ffc64940db28693c1836365b026d51f1a66fecad
    Author: crusaderky <crusaderky@gmail.com>
    Date:   Mon Jun 15 14:36:35 2020 +0100

        tweak test

    commit 106993c4476c789636aed34d7c405034c6797cc8
    Merge: ca9adac 80e9c19
    Author: crusaderky <crusaderky@gmail.com>
    Date:   Mon Jun 15 14:12:54 2020 +0100

        Merge branch 'v013' into issue1112

    commit ca9adac7279da05e0390f91b2da7f24bc157f001
    Author: crusaderky <crusaderky@gmail.com>
    Date:   Mon Jun 15 14:10:51 2020 +0100

        Test

Until this commit, `int` and `float` were special types in Pint
(just as they are in Python). Numbers were parsed from strings
as int/float from the definition files and from user provided
strings; and exponents of units were also stored as int/float.

This commit change this by adding a new argument (`non_int_type`)
to classes and methods. It indicates how numeric values will be parsed
and defaulted. Any numerical class can be used such as `float` (default),
Decimal, Fraction.

This argument will be found in the following places
1. UnitRegistry: used for parsing the definition files and any
  value provided as a string.
2. UnitsContainer: used to compare equality with strings, multiply and
  divide by strings (which is equivalent to parse the string)
3. All methods OUTSIDE the UnitRegistry/Quantity that can parse
   strings have a `non_int_type` argument. (e.g. Definition.from_string)

Tests have been added for by duplicating most cases in `test_quantity.py`.
(Some tests have been deleted such as those dealing with numpy.)
The new file `test_non_int.py` run the tests for `Decimal`, `Fraction` and
`float` (which is redundant but is kept as a crosscheck for the implementation
of this testsuite)

BREAKING CHANGE: `use_decimal` is deprecated.
Use `non_int_type` keyword argument when instantiating the registry.
 >>> from decimal import Decimal
 >>> ureg = UnitRegistry(non_int_type=Decimal)