(neilen, charles) Prepare katcp library for release of 0.5.1

git-svn-id: https://katfs.kat.ac.za/svnDS/code/katcp-python/trunk@16848 b56c7a7d-ac47-0410-a905-b6f7de78896a
(nmarais, to be reviewed) Fix memory leak due to strategies that use sampling
reactor staying behind in the 'next event' heap

git-svn-id: https://katfs.kat.ac.za/svnDS/code/katcp-python/trunk@17539 b56c7a7d-ac47-0410-a905-b6f7de78896a
(neilen, paul) Review code for  memory leak fix Mantis 2291

git-svn-id: https://katfs.kat.ac.za/svnDS/code/katcp-python/trunk@17544 b56c7a7d-ac47-0410-a905-b6f7de78896a
Merge branch 'master' of github.com:ska-sa/katcp-python
Update docs and version for v0.5.2 release