Final 2.5.0 release (PyPi published)

2.5.0 - Converters, construct_dict, get_function_params

 - Includes commit 12da829 which enables 2.5.0 to function fully on Python 3.6 and 3.7 (prior to this commit
   some tests only worked on 3.8+)

```
commit 12da829
Date:   Thu Dec 5 02:39:32 2019 +0000
Add local_tests.sh, fix get_function_params on older python

     - Added `local_tests.sh` for running the unit tests on multiple python versions locally
     - Added `OrderedDictObject` to collections module, since python versions before 3.8 cannot reverse a normal dict.
     - Add unit tests for ordered dict object
     - Adjusted `get_function_params` to use the new OrderedDictObject (fixes failing tests on older python versions)
```

**New Features / Additions**

 - `privex.helpers.common`
    - Added `get_function_params` - which extracts and filters a function/method or class constructor's parameters, and
      outputs them in a dictionary
    - Added `construct_dict`, which allows you to either construct a class, or call a function using a dictionary of keyword arguments,
      using `get_function_params` to detect what arguments the class/function/method can take, including any parent classes, then
      filtering out any keyword arguments which would otherwise be rejected and cause a TypeError.
    - Added `_filter_params`, a private function used by the aforementioned functions to filter a dictionary or iterable of Parameter objects.
 - New module `converters`, containing functions/classes designed to convert/parse one type into another
    - `convert_datetime` converts both string date/time's as well as unix timestamps into `datetime.datetime` objects using `dateutil.parser`
    - `convert_unixtime_datetime` converts specifically UNIX epoch timestamps (can be string, int, float, Decimal etc.) into `datetime.datetime` objects,
      and is used by `convert_datetime` to handle unix timestamps.
    - `convert_bool_int` converts booleans `True` / `False` as well as string / int versions into integers 1 (true) and 0 (false)
    - `convert_int_bool` is mostly an alias to `is_true`, but exists for convenience and semantics (if there's a convert_bool_int, why not a convert_int_bool?)

**Changes / Updates**

 - Shrank the rather large copyright notice in most modules down to the small copyright block, and instead of dumping the whole X11 / MIT License text in there,
   the licence block simply states `License: X11 / MIT`. This should make the docs a bit more readable.
 - Added `python-dateutil` to the `Pipfile`
 - For sanity reasons, `python-dateutil` has been added to the `install_requires` (meaning it's auto-installed when you install privex-helpers). The package is relatively
   small and depends on just `six`, weighing in around 500kb (python-dateutil = 468kb, six = 36kb).

   It may be removed and refactored into a setup.py extra at a later point, but for now it's small and commonly required enough that it can be a dependency.
 - Added `dateutil` to the sphinx intersphinx mapping
 - Possibly other small changes I forgot to include

**Testing**

 - Added new test case `TestInspectFunctions` to test_general, which tests the new `get_function_params` and `construct_dict` functions.
 - Added new test module `test_converters.py` which contains test cases for the new converters module
    - `TestConvertDate` covers date/time related converters such as `convert_datetime` and `convert_unixtime_datetime`
    - `TestConvertGeneral` covers other converters that don't fit into a specific category (or would otherwise be pointless to categorize)