feat(utils): add few string utils

sonic-radiance.love/core/utils/init.lua

@@ -28,5 +28,6 @@ return {
   math        = require(cwd .. "math"),
   graphics    = require(cwd .. "graphics"),
   filesystem  = require(cwd .. "filesystem"),
-  table       = require(cwd .. "table")
+  table       = require(cwd .. "table"),
+  string      = require(cwd .. "string")
 }

sonic-radiance.love/core/utils/string.lua

@@ -0,0 +1,26 @@
+local String = {}
+
+function String.isEmpty(pString)
+    return (pString == "" or pString == nil)
+end
+
+function String.split(pString, pPattern)
+    local Table = {}  -- NOTE: use {n = 0} in Lua-5.0
+    local fpat = "(.-)" .. pPattern
+    local last_end = 1
+    local s, e, cap = pString:find(fpat, 1)
+    while s do
+       if s ~= 1 or cap ~= "" then
+      table.insert(Table,cap)
+       end
+       last_end = e+1
+       s, e, cap = pString:find(fpat, last_end)
+    end
+    if last_end <= #pString then
+       cap = pString:sub(last_end)
+       table.insert(Table, cap)
+    end
+    return Table
+ end
+
+return String