Q3dfit

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Patches:
- Fixed bug in initialization of line ratio constraints. Added text
better describing these constraints in notebooks.
- Fixed error in multicore processing due to conflicting
filenames. math.py, utility.py, and q3dfit.py renamed to q3dmath.py,
q3dutil.py, and q3df.py.
- All inputs to LMFIT now float32 to prevent numerical errors.
- Added sphinx processing for readthedocs.
- Fixed link errors in readthedocs.
- Bugfix: checkcomp now working properly.
- Misc. bugfixes.

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Release for JWST Cycle 2 Call for Proposals. MIR fitting still in
progress due to lack of Q3D MIRI data, pending resolution of MIRI
grating issue.
- Software tested on NIRSpec data of J1652.
- Initialization dictionary converted to q3din class.
- Fit output now q3dout class.
- Plots of fit results moved to methods of q3dout class.
- Renaming / combining / clean-up of files.

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First release.