Adding `abacus`.c/h.

`abacus.h` contains basic package information stored in macros, and
provides the provides the prototype for function `abacus_preamble`,
which returns a formated string of package info.
Adding `get_c_array` prototype to `array_utils.h`
Updating program help messaging.

Updating messaging for `eureject`, `dpdraw`, and `intpart`.
Help messages now get printed to stderr, rather than stdout. All
three programs now display a standard ABACUS preamble message,
and also give a brief description of what they do.
Updating makefiles.