Welleng

There's issues with the the release filenames for 'python-fcl' for Windows. For now, 'python-fcl' needs to be manually installed in Windows.

- modified the `setup.py` file with a conditional requirement: `python-fcl` and `python-fcl-win32` if the host OS is Windows.
- will add instructions on how to install on Windows soon.

- Added `interpolate_survey` function to `connector` module for interpolating fixed interval stations on sparse surveys.
- Updated the `requirements.txt` to include `python-fcl-win32` for Windows installs - instructions on how to install `welleng` on Windows coming soon.
- Bug fixes.