Fix markdown.lua to work with LUA 5.2

The `setfenv` variable is unavailable in LUA 5.2, so call it conditionally.
Merge pull request #69 from gns-ank/patch-1

Fix markdown.lua to work with LUA 5.2
issue #70 crash
no longer any need for setfenv in markdown.lua
set tag in module can be used to set rendering properties etc of an individual module, e.g 'set no_return_or_parms=true'
Merge branch 'master' of github.com:stevedonovan/LDoc
finally fixed issue #32 (sorry Eric). Can now dump non-modules like scripts
issue #64: use 'sort=true' in config.ld to sort items in sections
a partial solution for issue #73: ldoc.module_file to pick master modules when present
better soln for issue #73: partial sorting for all processed files
support for generating Markdown; basic support for Moonscript
Moonscript: support for modules using with statement; optionally ignore colon as part of an identifier
support for Moonscript fat vs thin arrows; tools.get_parameters also returns last token found; lang.method_call generalization
partial file list sorting refactor was borked
new classmod tag for defining modules that just export one class (experimental)
issue #66: better error message for non-luadoc behaviour; now controlling backticks in the docs better
issue #77: 'See also' in template
fix #84; also no_space_before_args=false to stop ldoc putting space between name and arglist of functions
fix issue #79: will not allow a module as a type. Plus, add reference lookup for lfs and lpeg
a list of comma-separated items can appear after a see tag; fixed problem with references to Lua global functions from last commit