Python-datemath

* [FIX] [Issue 28](https://github.com/nickmaccarthy/python-datemath/issues/28)
* `datemath()` object now returns the expected `datetime` object instead of an `Arrow` object
* added tests to catch invalid object types of helpers

* skipped due to name conflict on pypi, all changes in this are from `1.5.3`

* [FIX] [Issue 25](https://github.com/nickmaccarthy/python-datemath/issues/25) - Fixed an issue where if you provided an invalid timestamp, i.e. `datemath('2')` you would not get an DateMathException back. Also bumped dependencies.

* [FIX] [Issue 21](https://github.com/nickmaccarthy/python-datemath/issues/21) - Fixed an issue where if timezone offset was in a datetime string (ISO8601), the timezone of the returned datemath object would be UTC and not the timezone as specified in the datetime string.

* [FIX] [Issue 15](https://github.com/nickmaccarthy/python-datemath/issues/15) - Fixed issue with parser finding invalid timeunits and throwing correct errors
* [NEW] [Issue 16](https://github.com/nickmaccarthy/python-datemath/issues/16) - Added support for parser to accecpt a epoch/unix timestamp but throw an error on epoch milli's since arrow can't support that.

* [FIX] [Issue 12](https://github.com/nickmaccarthy/python-datemath/issues/12) - missing VERSION.txt. Added MANIFEST.in for sdist build
* [FIX] [PR 13](https://github.com/nickmaccarthy/python-datemath/pull/13) - Fix `BaseException` to `Exception` inheritence, thank you for your contribution yury-primer!