Pre-Release of Ride 4.6

WARNING: This is a pre-release version of Ride 4.6: it is possible that functionality may be added, removed or altered; we do not recommend using pre-release versions of Ride in production environments.

Changelog:
Fix silly error where I updated the pre-20.0 code, not the 20.0 onwards code
#1336 dyalog_readme.htm will appear in /files, not /
Merge pull request #1342 from Dyalog/hlp_url
Update Getting started URL
Update help URLs for v20.0
Merge pull request #1338 from Dyalog/build_tmpdir
Exclude pid from tmpdir and use same path for Jenkins
Corrected JOB_NAME variable
Change build tmp dir to support parallel builds
Merge pull request #1340 from Dyalog/hlp_nohelp
Don't show help if no URL returned from interpreter
Fix #1274 (specify APLAN colours)