Add devel/lua-luacheck, linter and static analyzer for lua

Provides linting and static analysis for Lua 5.1, Lua 5.2, Lua 5.3 and
LuaJIT. A patch was required to allow luacheck and luacheck.lua to be
symlinked into ${PREFIX}/bin, which I have submitted upstream.

Checked with: portlint
Tested with: Poudriere (head, amd64)
Tested with: Poudriere (stable/11, amd64)
Tested with: Poudriere (11.1-R, i386) [lwhsu]
Tested with: Poudriere (10.4-R, amd64+i386) [lwhsu]
Reviewed by: lwhsu
Approved by: lwhsu (ports)
Differential Revision: https://reviews.freebsd.org/D14467