Spec2nexus

* `197 <https://github.com/prjemian/spec2nexus/issues/197>`_
plugins: handle empty empty O0 or P0 list
* `195 <https://github.com/prjemian/spec2nexus/issues/195>`_
drop CII badge: not useful to spec2nexus
* `190 <https://github.com/prjemian/spec2nexus/issues/190>`_
writer: link content into NXinstrument group
* `51 <https://github.com/prjemian/spec2nexus/issues/51>`_
plugins: interpret Gn control lines

* `181 <https://github.com/prjemian/spec2nexus/issues/181>`_
plugins: revised technique to load control line handlers

**NEW**

* support for ``UXML`` metadata
* support for ``hklscan`` scans
* improved support for ``mesh`` and ``hklmesh`` scans

* `159 <https://github.com/prjemian/spec2nexus/issues/159>`_
handle UXML metadata control lines
* `155 <https://github.com/prjemian/spec2nexus/issues/155>`_
module: writer - recognize hklscan
* `150 <https://github.com/prjemian/spec2nexus/issues/150>`_
module: writer - increase coverage of unit tests: mesh, hklmesh
* `148 <https://github.com/prjemian/spec2nexus/issues/148>`_
module: eznx - increase coverage of unit tests

* `170 <https://github.com/prjemian/spec2nexus/issues/170>`_
describe how to write & load Control Line Handler plugins
* `169 <https://github.com/prjemian/spec2nexus/issues/169>`_
announce deprecation of python 2
* `165 <https://github.com/prjemian/spec2nexus/issues/165>`_
resolve conda build error
* `149 <https://github.com/prjemian/spec2nexus/issues/149>`_
unit tests: ``units`` module

**API change**:
Changed how plugins are defined and registered.
Custom plugins must be modified and import code revised
to work with new system.

* `168 <https://github.com/prjemian/spec2nexus/pull/168>`_
plugins are now self-registering
* `166 <https://github.com/prjemian/spec2nexus/issues/166>`_
fix conda packaging

NOTE: conda package is broken (no plugins directory).
Only use ``pip install spec2nexus`` with this release.

* `164 <https://github.com/prjemian/spec2nexus/issues/164>`_
post conda packages to `aps-anl-tag` channel
* `161 <https://github.com/prjemian/spec2nexus/issues/161>`_
read files with no E control line
* `156 <https://github.com/prjemian/spec2nexus/issues/156>`_
LGTM code review
* `153 <https://github.com/prjemian/spec2nexus/issues/153>`_
LGTM code review