libraries/libbladeRF: Fix documentation build

Some of the documentation is built with pandoc using
some custom bash script. We need to fixup the shebang
for that script to correctly run. Other parts of the
documentation is built using help2man and doxygen.

We also make libtecla a dependency for interactive
help support.

There is an upstream bug that makes builds fail when
pandoc is in PATH. Most importantly however, the
man pages should now build and install correctly.

Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>