Add basic infrastructure for unit testing

Tests will be written using the [moonscript](http://moonscript.org/) language,
a lua 'dialect' that is whitespace-significant and has a syntax similar to
coffeescript. The test framework used is [busted](http://olivinelabs.com/busted/),
a bdd framework for lua/moonscript.

Luajit has a nice ffi module, which lets lua programs link shared libraries and
call it's functions without writing any C code.

To take advantage of this fact for testing C functions, a new target was added
to CMakeLists.txt, which compiles neovim as a shared library that is loaded by
the process running the tests.

This commit adds necessary code for downloading and installing a lua package
manager(luarocks) locally. It wasn't added as a subtree because there are quite
a few blobs in its source tree.

test/unit/helpers.moon

@@ -0,0 +1,35 @@
+ffi = require 'ffi'
+
+-- load neovim shared library
+libnvim = ffi.load './build/src/libnvim-test.so'
+
+-- Luajit ffi parser only understands function signatures.
+-- This helper function normalizes headers, passes to ffi and returns the
+-- library pointer
+cimport = (path) ->
+  -- Can't parse some of vim types, perhaps need to define those before
+  -- automatically importing to ffi
+
+  -- header_file = io.open path, 'rb'
+  -- header = header_file\read '*a'
+  -- header_file.close!
+  -- header = string.gsub header, '#include[^\n]*\n', ''
+  -- header = string.gsub header, '#ifndef[^\n]*\n', ''
+  -- header = string.gsub header, '#define[^\n]*\n', ''
+  -- header = string.gsub header, '#endif[^\n]*\n', ''
+  -- ffi.cdef header
+
+  return libnvim
+
+-- take a pointer to a C-allocated string and return an interned
+-- version while also freeing the memory
+internalize = (cdata) ->
+  ffi.gc cdata, ffi.C.free
+  return ffi.string cdata
+
+return {
+  cimport: cimport
+  internalize: internalize
+  eq: (expected, actual) -> assert.are.same expected, actual
+  ffi: ffi
+}

test/unit/misc1.moon

@@ -0,0 +1,38 @@
+{:cimport, :internalize, :eq, :ffi} = require 'test.unit.helpers'
+
+misc1 = cimport './src/misc1.h'
+cstr = ffi.typeof 'char[?]'
+
+-- TODO extract constants from vim.h
+
+describe 'misc1 function', ->
+  describe 'fullpathcmp', ->
+    ffi.cdef 'int fullpathcmp(char *s1, char *s2, int checkname);'
+    fullpathcmp = (s1, s2, cn) ->
+      s1 = cstr (string.len s1) + 1, s1
+      s2 = cstr (string.len s2) + 1, s2
+      misc1.fullpathcmp s1, s2, cn or 0
+
+    f1 = 'f1.o'
+    f2 = 'f2.o'
+    f3 = 'test/f1.o'
+    FPC_SAME = 1
+    FPC_DIFF = 2
+    FPC_NOTX = 4
+    FPC_DIFFX = 6
+    FPC_SAMEX = 7
+
+    before_each ->
+      -- create the three files that will be used in this spec
+      (io.open f1, 'w').close!
+      (io.open f2, 'w').close!
+      (io.open f3, 'w').close!
+
+    after_each ->
+      os.remove f1
+      os.remove f2
+      os.remove f3
+    
+    it 'returns FPC_SAME when passed the same file', ->
+      eq FPC_SAME, (fullpathcmp f1, f1)
+