rename cache.WeakCacheObject to cache.Immutable
start new unit testing system
add makefile
replace Simplex._split_by_child by ._child_subsets
rename simplex to reference
generalize point, line, triangle, tet to simplex
introduce vertex ischeme, rename Product to Tensor
introduce ReferenceElement, TrimmedElement
rewrite grid, add enumerate_nd
Merge commit 'a215743945750209b806674ec777b69e6c0b2253' into sane
major change: remove parent, context from elem obj
add set functions
Merge commit '7d7a74ce36260221cd90d69635294e2cae77dbbd' into sane
start topology cleanup
reactivate pointset cache
fix unstructured boundaries