build: general improvements

Allow customising the bin and manual page dirs.

Signed-off-by: Paul Wise <pabs3@bonedaddy.net>
Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Ignore the generated manual page

Signed-off-by: Paul Wise <pabs3@bonedaddy.net>
Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
build: avoid non-portable install -D

BSD install doesn't understand the -D option.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>