This is an implementation of POSIX bc that implements GNU bc extensions, as
well as the period (".") extension for the BSD flavor of bc.

bc is an arbitrary precision numeric processing language.  Its syntax is
similar to C but differs in many substantial areas.  It supports interactive
execution of statements.  The bc utility is included in the POSIX 1003.1-2008
standard.

This bc also includes an implementation of dc in the same binary, accessible
via a symbolic link, which implements all FreeBSD and GNU extensions.  If a
single dc binary is desired, bc can be copied and renamed to dc.

The "!" command is omitted; I believe that it poses security concerns and
that such functionality is unnecessary.