The issue with building out-of-tree was that some pages were generated by autoconf in $(builddir) and others were as-in in $(srcdir). While it was possible to use the right combination of $(builddir)/$(srcdir), just move everything as .in and generate every page during the configure step.

if telescope is started with an url while there is already another instance of it running and the -S flag is not provided, the link will be automagically opened into the running instance of telescope. Telescope now listens on a UNIX domain socket in ~/.telescope/ctl (or ~/.cache/telescope/ctl if XDG is used) for commands.

it's not spelled `util.h' because otherwise it'd get included instead of /usr/include/util.h

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.