Commit Briefs
provide HOSTCC and HOSTCFLAGS variables to simplify cross-compilation
pagebundler is a helper that needs to be built with the *host* compiler because it's used to generate some sources. In normal situations, HOSTCC and HOSTCFLAGS are just ${CC} and ${CFLAGS}, but folks that cross-compile can specify there the host compiler and flags to successfully build telescope. The idea is largely based on what gforth does: it re-uses ${CFLAGS} for the host compiler though, while I'm adding an extra variable for that.
move help to its own file
in order to do so, we also have to export some internal variables from ui (the width and height of the window). Not the best possible outcome, but are used only in recompute_help, and can be dropped later. Also, move wrap_page to wrap.c.