Make different fitting settings "parameterized"

[jacobfc]

Currently, settings for the VAMP fits (chi-squared thresholds, number of attempts at convergence, etc.) are hard-coded into VPfits.py .

It would be useful to pass VAMP a configuration file, that would specify these various parameters. This would allow users to run VAMP with various settings more easily (e.g. a "quick" VAMP setting with less stringent convergence criteria, or a "thorough" setting with more attempts at convergence before giving up, etc.)

I believe this should be done so that there are default values in VAMP, but individual values can be over-ridden using a config file (rather than forcing users to specify a bunch of parameters which they may not understand fully).

Things that I can think of which would be useful to specify:

• chi-squared limit ("chi_limit" in fit_spectrum() )

• number of attempts before settling for a fit above "chi_limit"

• chi-squared maximum (before forcing VAMP to add a new line)

• number of attempted fits before forcing VAMP to add a new line

• maximum number of components to allow a "region" to have (a default of ~10?)

• flux floor (value flux is set to if flux <= 0)

• (possibly also some MCMC settings for more advanced users, who know how MCMC chains work?)