Some content was only documented in `documentation`

[ericonr]

I suggested removal of the old documentation directory in #506 , but didn't realize there were a few files there which weren't available anywhere else.

git show --name-status 1a9135976b4bc75bfdfe1ed7516a3e7d29e08e6b | grep html | sed "s,D.*documentation/\(.*\).html,\1.rst," > old-docs

~/p/e/a/ADCore HEAD λ for f in (cat old-docs)
                          if [ -z (git ls-files | grep $f) ]
                              echo $f
                          end
                      end

results in:

CSS-BOY_screens.rst
FindingAreaComponents.rst
NDPosPlugin.rst
areaDetector.rst
areaDetectorDoc.rst
areaDetectorReleaseNotes.rst
areaDetectorTimeStampSupport.rst
pluginDoc.rst

Out of these, I believe that the following should be converted to rst so they can be included in the current documentation:

• FindingAreaComponents
• areaDetectorTimeStampSupport

NDPosPlugin is a false positive because the rst file is called NDPluginPos, and the rest can simply be discarded.

I noticed this while looking at #535

[ericonr]

If anyone wants to tackle these files, I believe the timestamp support one is outdated now because the updateTimestamps function is available, so it isn't necessary to open code the timestamp processing.