Remove the generation of HAL support files

Remove the code supporting the generation of HAL FDI file. This is
the first commit of a set to address Github issue #99
Remove the remaining HAL files and references

Remove the remaining build rules, source code and documentation related
to the FreeDesktop Hardware Abstraction Layer (HAL) support. For the
record, with this HAL implementation, NUT drivers were sending data
over DBus (Closes: #99)
Add a note on Hardware Abstraction Layer removal
Merge pull request #105 from networkupstools/hal_removal

Hal removal