Spectrum filtering

[maxbriel]

This implements the usage of pysynphot build-in and custom filters with BPASS spectra. The added functions are:

• load_bandpass: load build-in bandpass or custom filter file
• apply_bandpass: apply the bandpass to a spectra
• get_spectrum: get a spectra directly from BPASS data
• flux_to_vegamag: calculates the vegamagnitude using the pysynphot Vega spectrum
• import_custom_filter: import a custom filter file

unit tests are included in test_spec and are based on manual calculations or definitions.

Furthermore, I cleaned up the docs folder and added a conf.py file, such that it is able to compile locally. This does move the Makefile and make.bat into the docs directory. Although, it does not seem to be the most up-to-date version of the documentation and ipynb do not run correctly due to the data folder being in a different location. However, these issues can be fixed easily. It would also be possible to remove the docs it these are not used, but I would not recommend that.

[maxbriel]

I have never worked with Travis and am not sure how to set the correct environment variables to be able to use pysynphot

[HeloiseS]

I will look into Travis.

To be honest, I have on my to-do list the idea of moving away from travis and using something native to github but that's my own problem :laughing:

[maxbriel]

Thanks for the feedback! I will get to it!

The Travis problem is two-fold. I think the correct path is now set, but some pysynphot essential files are still missing. I'm looking into it!