Client lua api documentation: .md -> .txt

For consistency, and for much improved access on Github.

On Github:
.md disables being able to link to a line, needed daily when
quickly referring people to particular lines.
Search returns results in .md files, but you cannot then click
the line number to go to that line in the document, making searching
difficult.
Line numbers are not displayed for .md documents.
This commit is contained in:
paramat 2017-11-28 23:22:49 +00:00 committed by paramat
parent b312ab4455
commit 18b914ac74