Add from_elem for StorageByInts2.
Add convenience constr for NBSideInclusions.
Add test for new StorageByInts2 constr.
Merge branch 'master' of https://github.com/scharris/WGFEM-Rust
Merge branch 'master' of https://github.com/scharris/WGFEM-Rust
Preliminary triangle mesh, not finished.