- Added AsciiCharset for matching ascii characters quickly.

- Added `String.trim_charset`.

lib/std/core/string.c3

@@ -1,6 +1,5 @@
 module std::core::string;
-import std::io;
-import std::core::mem::allocator;
+import std::io, std::ascii;
 
 
 typedef String @if(!$defined(String)) = inline char[];
@@ -219,6 +218,23 @@ fn String String.trim(self, String to_trim = "\t\n\r ")
     return self.trim_left(to_trim).trim_right(to_trim);
 }
 
+<*
+ Remove characters from the front and end of a string.
+
+ @param [in] self : `The string to trim`
+ @param to_trim : `The set of characters to trim, defaults to whitespace`
+ @pure
+ @return `a substring of the string passed in`
+*>
+fn String String.trim_charset(self, AsciiCharset to_trim = ascii::WHITESPACE_SET)
+{
+	usz start = 0;
+	usz len = self.len;
+	while (start < len && to_trim.contains(self[start])) start++;
+	while (len > start && to_trim.contains(self[len - 1])) len--;
+    return self[start..len - 1];
+}
+
 <*
  Remove characters from the front of a string.