Add PCRE to support regular expressions

Use regular expressions instead of Lua patterns for find and replace editor commands.

Syntax files can now use regex or Lua patterns as before keeping backward compatibility for plugins.

data/core/regex.lua

@@ -0,0 +1,69 @@
+
+-- So that in addition to regex.gsub(pattern, string), we can also do 
+-- pattern:gsub(string).
+regex.__index = function(table, key) return regex[key]; end
+
+regex.match = function(pattern_string, string, offset, options)
+  local pattern = type(pattern_string) == "table" and
+    pattern_string or regex.compile(pattern_string)
+  return regex.cmatch(pattern, string, offset, options)
+end
+
+-- Will iterate back through any UTF-8 bytes so that we don't replace bits 
+-- mid character.
+local function previous_character(str, index)
+  local byte
+  repeat
+    index = index - 1
+    byte = string.byte(str, index)
+  until byte < 128 or byte >= 192
+  return index
+end
+
+-- Moves to the end of the identified character.
+local function end_character(str, index)
+  local byte = string.byte(str, index + 1)
+  while byte >= 128 and byte < 192 do
+    index = index + 1
+    byte = string.byte(str, index + 1)
+  end
+  return index
+end
+
+-- Build off matching. For now, only support basic replacements, but capture
+-- groupings should be doable. We can even have custom group replacements and
+-- transformations and stuff in lua. Currently, this takes group replacements 
+-- as \1 - \9.
+-- Should work on UTF-8 text.
+regex.gsub = function(pattern_string, str, replacement)
+  local pattern = type(pattern_string) == "table" and
+    pattern_string or regex.compile(pattern_string)
+  local result, indices = ""
+  local n = 0
+  repeat
+    indices = { regex.cmatch(pattern, str) }
+    if #indices > 0 then
+      n = n + 1
+      local currentReplacement = replacement
+      if #indices > 2 then
+        for i = 1, (#indices/2 - 1) do
+          currentReplacement = string.gsub(
+            currentReplacement, 
+            "\\" .. i, 
+            str:sub(indices[i*2+1], end_character(str,indices[i*2+2]-1))
+          )
+        end
+      end
+      currentReplacement = string.gsub(currentReplacement, "\\%d", "")
+      if indices[1] > 1 then
+        result = result .. 
+          str:sub(1, previous_character(str, indices[1])) .. currentReplacement
+      else
+        result = result .. currentReplacement      
+      end
+      str = str:sub(indices[2])
+    end
+  until #indices == 0 or indices[1] == indices[2]
+  return result .. str, n
+end
+