Splitting fe.[ch]pp

[mlstowell]

There seems to be a consensus forming around the idea that fe.cpp and fe.hpp are growing too large.

[pform:GitHub/mfem-master/fem] stowell1% wc -l fe.?pp
   13489 fe.cpp
    3493 fe.hpp
   16982 total

There are many ways these might be split into more manageable sizes but to get the conversation started I'll propose the following:

• fe.[ch]pp to contain the FiniteElement base class and any other common definitions or code
• fe_h1.[ch]pp to contain the H1 basis functions
• fe_l2.[ch]pp to contain the L2 basis functions
• fe_nd.[ch]pp to contain the ND basis functions
• fe_rt.[ch]pp to contain the RT basis functions
• fe_misc.[ch]pp to contain other classes that don't fit naturally in the above files

Other ideas are certainly welcome. For something like this there seems to be little point in starting a branch or a PR until we reach some sort of an agreement on how best to split things. I look forward to hearing people's ideas on this.

Attn: @dylan-copeland, @tzanio, @v-dobrev

[v-dobrev]

This sounds good to me. The only remaining question for me is what classes and functions stay in fe.[ch]pp and what go to fe_misc.[ch]pp. If there are just a few things to go in fe_misc.[ch]pp we can just keep them in fe.[ch]pp.

[tzanio]

Mark, can you take a crack at your proposed split when you get a chance and report the resulting sizes?

My feeling is that fe_misc.[ch]pp will probably be the largest.

[mlstowell]

A draft of this suggestion (with a few modifications) has been started in PR #2335