Allow user customisation of columns in bpp and bcm tables

[TomWagg]

I've added two arguments to Evolve.evolve(), bpp_columns and bcm_columns. Users can specify a list of columns to include in either table, by default it will use the current setup so no breaking changes with this 😅 I've made the changes directly in the Fortran as well so this will perhaps cut down on RAM usage during the run.

The only change I made that alters the default behaviour is to report kstar_x and evol_type as integers instead of floats, which I think makes sense?

(Selfishly motivated by TomWagg/cogsworth#86 🙃)

Implementation details

The way it works is:

• Define a list of all possible columns (in python and in fortran files)
• Convert user input into a number of columns in each table and indices of the variables you want to add
• In writetab (new function that combines writebpp and writebcm in a simpler way), access the specific variables in the order the inds specify

This means I had to define some new variables in const_bse.h and also change the calling of writebpp and writebcm everywhere.

Demo

Default behaviour

Specifying certain columns

[katiebreivik]

amazing! We can merge this in for now but we should be sure to add in some docs for providing the kwargs for the columns to the evolve call.