Support for some function expressions / stateful rules

[joshfried-aws]

Issue #, if available:
#295
#140

Description of changes:
Refactor all occurrences of &'value PathAwareValue to Rc<PathAwareValue> while this has a performance impact, due to the way functions are computed we have no other choice, since &'value lifetime refers to when the specific value was parsed, and thus values that are computed can never meet that requirement. This also allowed us to remove the lifetime constraints on many structs and functions. This refactor also made us add a dependency on the Rc feature in the serde crate

Refactored the PathTree struct from pub(super) type PathTree<'report, 'value> = BTreeMap<&'value str, Vec<std::rc::Rc<Node<'report, 'value>>>>; topub(super) type PathTree<'report, 'value> = BTreeMap<String, Vec<std::rc::Rc<Node<'report, 'value>>>>;

this is a direct result of the change mentioned above

Add support for the following functions

count -
takes a single query result argument as a parameter and returns the number of occurrences. For examples please refer to

json_parse -
takes a single query result and attempts to convert a string into a json object.

regex_replace -
takes 3 arguments the first is a query result, the 2nd is the extracted regular expression, and the third is the replacement regular expression

substring -
takes 3 arguments the first is a query result, the 2nd is the starting index (inclusive), the 3rd is the last index (non inclusive)

to_lower -
takes a single query result and returns a string that is all lowercase

to_upper -
same as above except the returned string is all uppercase

url_decode -
takes a single queryy result and returns a url decoded version of the string

ex:This%20string%20will%20be%20URL%20encoded => "This string will be URL encoded"

for examples of these functions see the accompanying guard files

---

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license