Input file checker

[RolfSander]

When working with KPP, bugs are often difficult to find, especially when
some limit has been exceeded and KPP crashes with a segmentation fault.
Today, I spent a lot of time until I noticed that some equations were
longer than MAX_EQNLEN allows (see #94).

I suggest to write a checker for KPP input files. This can be a small
python script which checks if the input file is consistent with
MAX_EQNLEN and other MAX_* limits from gdata.h.

I hope I'll be able to find the time soon to create a first prototype...