add xembed wrapper utility

xembed will cause a command to attempt to XEmbed into the window given
by the environment variable XEMBED, so long as it is in the foreground
of its controlling terminal. This causes a process to effectively take
the place of the terminal window, unless it is backgrounded.

Signed-off-by: Christoph Lohmann <20h@r-36.net>

Introduce ARG* macros to simplify arg handling.

fixing README and Makefile.

removing surf-stuff, distributing tabbed on its own.

start writing tabbed.

moving config.h to config.def.h.

merged, now has download bar, other misc fixes

rearranging, adding initial keyboard support.

supporting multiple windows per instance

Initial Commit.