Merge pull request #120 in CASA/casa from bugfix/CAS-10121 to master
* commit '948bcb7a7aab99d25e6f028e1153d5e44a1f4eec':
add banner about online documentation
add doc("start") option and message, clean up local doc URLs
adjust doc and toc.xml URLs
add instructive user output to the doc( ) command