IndentationBear: Move generic methods to new file

Move Generic methods and exceptions from IndentationBear
to RangeHelpers and CustomExceptions. Also it modifies
the bear to support indent based on keywords.

bears/general/CustomExceptions.py

@@ -0,0 +1,11 @@
+class UnmatchedIndentError(Exception):
+
+    def __init__(self, open_indent, close_indent):
+        Exception.__init__(self, 'Unmatched ' + open_indent + ', ' +
+                           close_indent + ' pair')
+
+
+class ExpectedIndentError(Exception):
+
+    def __init__(self, line):
+        Exception.__init__(self, 'Expected indent after line: ' + str(line))