[Ohrrpgce] SVN: teeemcee/9955 Add script commands for line slices

[subversion at HamsterRepublic.com]

teeemcee
2018-01-11 09:14:22 -0800 (Thu, 11 Jan 2018)
200
Add script commands for line slices

Still have to add some basic testcases to check these actually work

I'm not adding or extending any more Change*Slice functions. Instead, I started
using methods.
---
U   wip/const.bi
U   wip/docs/plotdict.xml
U   wip/plotscr.hsd
U   wip/scriptcommands.bas
U   wip/scriptcommands.bi
U   wip/slices.bas
U   wip/slices.bi
U   wip/whatsnew.txt