Changing from completion to ligo_channels.
Also changed the function names from complete to completion.

Implemented w/ pybind11.

Correct the comparision used so that lower/upper bounds work

See merge request cds/channel_completion!3

The comparision function did not work properly.  Give it the length
of the expected key, and do not require the a specific input to the
comparision to be the search key.

This had caused issues where the key was not in the expected argument,
allowing strings that were shorter than the key length to be selected
as output.

System tests

See merge request cds/channel_completion!2

Added probe to the completion list.

This addes two new build/test requirements boost iterators and pstreams.

As there are several hundred thousand EPICS channels that are not recorded
in the frame, to do channel completion for EPICS needs more than the NDS
channel list.  This splits the system into supporting two databases.

Environment variables change from CHAN_LIST to EPICS_CHAN_LIST and
NDS_CHAN_LIST.

The database is allowed to have extra information following the channel
on each line, as long as a space is used to separate the extra data from
the channel.

Added tests against the ligo_channel_completion binary.

Symlink at install time

See merge request cds/channel_completion!1

if /usr/share/bash-completion/... is used, a symlink is needed per command being completed.

Bring in the catch2 test frame work.  Licensed under BOOST 1.0.

Make the main logic a library, so that it can be tested.  Add initial tests.

Name everything ligo_channel_completion.
Put the executable in /usr/lib.
Put the bash script in /usr/share/bash-completion/completions.

With bash auto completion if only one entry is returned it is assumed
to be the final completion.  This make sense if it is a full channel
name.  However if there is a series of one or more segments of the name
that are common through all the channels in question, you need to return
information that includes the next block that is different.  This is a
first reworking to handling this case.