Squashed 'sglib/' changes from 5b2bf65..07b48f5

07b48f5 Some separation of function under 'fem'
18d2737 Added comments to spatial_function stuff
b4b4b15 Fixed a bug introduced by "performance hints"
f298ee0 Moved and improved pde toolbox functions

git-subtree-dir: sglib
git-subtree-split: 07b48f5ca11c0a076ba64e0de5108c86c90f073c
Merge commit '5214be59a047b9f4ef6f4ac548b90b551ee44332'