Remove support python 2 from doc, requirements.txt and config
Replace unicode with str
Remove dbfpy folder and rename dbfpy3 to dbfpy
Remove compat file and remove python2 packages from dependency

* Add project release config and use Travis build stages.

Refs #378.

* Restructure project to use src/ and tests/ directories.

* Fix testing.

* Remove eggs.

* More fixes.

- isort and flake8 config
- manifest template update
- tox ini extension
- docs build fixes
- docs content fixes

* Docs and license cleanup.

The platform is not tested on Travis and it fails to run with:

    Processing ./.tox/dist/tablib-0.12.1.zip
    Collecting odfpy (from tablib==0.12.1)
    Collecting openpyxl>=2.4.0 (from tablib==0.12.1)
    Collecting backports.csv (from tablib==0.12.1)
      Using cached https://files.pythonhosted.org/packages/71/f7/5db9136de67021a6dce4eefbe50d46aa043e59ebb11c83d4ecfeb47b686e/backports.csv-1.0.6-py2.py3-none-any.whl
    Collecting xlrd (from tablib==0.12.1)
      Using cached https://files.pythonhosted.org/packages/b0/16/63576a1a001752e34bf8ea62e367997530dc553b689356b9879339cf45a4/xlrd-1.2.0-py2.py3-none-any.whl
    Collecting xlwt (from tablib==0.12.1)
      Using cached https://files.pythonhosted.org/packages/44/48/def306413b25c3d01753603b1a222a011b8621aed27cd7f89cbc27e6b0f4/xlwt-1.3.0-py2.py3-none-any.whl
    Collecting pyyaml (from tablib==0.12.1)
    Collecting pandas (from tablib==0.12.1)
      Using cached https://files.pythonhosted.org/packages/81/fd/b1f17f7dc914047cd1df9d6813b944ee446973baafe8106e4458bfb68884/pandas-0.24.1.tar.gz
        Complete output from command python setup.py egg_info:
        Traceback (most recent call last):
          File "<module>", line 1, in <module>
          File "/tmp/pip-install-F5lmAg/pandas/setup.py", line 732, in <module>
            ext_modules=maybe_cythonize(extensions, compiler_directives=directives),
          File "/tmp/pip-install-F5lmAg/pandas/setup.py", line 475, in maybe_cythonize
            numpy_incl = pkg_resources.resource_filename('numpy', 'core/include')
          File "tablib/.tox/pypy/site-packages/pkg_resources/__init__.py", line 1144, in resource_filename
            return get_provider(package_or_requirement).get_resource_filename(
          File "tablib/.tox/pypy/site-packages/pkg_resources/__init__.py", line 361, in get_provider
            __import__(moduleOrReq)
        ImportError: No module named numpy

        ----------------------------------------
    Command "python setup.py egg_info" failed with error code 1 in /tmp/pip-install-F5lmAg/pandas/

Allows all tests to pass.

As pandas is defined as an 'extra', use tox's 'extras' feature. This
requires tox 2.4+, so document that as well.

https://tox.readthedocs.io/en/latest/config.html#conf-extras

It is time to make it happen.

* Dropped Python 3.2 support

Recent dependencies are dropping Python 3.2 too.

* Replaced vendored openpyxl by a dependency

Thanks Tommy Anthony for the initial patch.