Add new string functions

Bro appears to have a rather limited list of built-in string functions. This lack of functionality makes it more difficult to write high performance Bro scripts that require large amounts of string processing.

Using Python as a model (https://docs.python.org/2/library/stdtypes.html#string-methods), I think Bro would benefit from having the following additional string functions:

• str.count - Return the number of non-overlapping occurrences of substring sub in the range

• str.find - Return the lowest index in the string where substring sub is found within the slice s[start:end].

• str.lstrip - Return a copy of the string with leading characters removed. The chars argument is a string specifying the set of characters to be removed.

• str.replace - Return a copy of the string with all occurrences of substring old replaced by new

• str.rstrip - Return a copy of the string with trailing characters removed. The chars argument is a string specifying the set of characters to be removed

• str.strip - Return a copy of the string with the leading and trailing characters removed. The chars argument is a string specifying the set of characters to be removed

Additionally, I think a find_all implementation that returned all indexes of the match would be helpful, as is described here: http://stackoverflow.com/questions/4664850/find-all-occurrences-of-a-substring-in-python .

I am willing to put forth the effort in writing these functions if the resulting code (assuming it meets all quality requirements) would be merged in.