unused code cleanup
[algo] Simplified halfspace generation

Some duplicate work was being done in the line rotation around the
origin. We used to handle only events with nonnegative labels, and
output a pair of antipodal hyperplanes for each such event. This,
however, is unnecessary, because events with labels i and (-1-i) are
already antipodal.
simplified event points and abstracted Vector_t

The simplification of the event points makes more useful in specialized
constructions like 3D.

The pulling the vector type out to a template is a step in allowing the
dimension to be fixed at compile time. Then, one could for example use
Vector_t = std::array<3, Number_t> in three dimensions and hope that the
compiler uses the extra knowledge to unroll loops where appropriate.
install headers under include/zonotope
initial support for double in hyperplanes
Vector_t as template
added missing changes for double
improved type support in C interface
minor modification of test.sage