Add support for big_decimal and big_integer objects

[jeaye]

Overview

Clojure supports BigInt and BigDecimal as numbers which can grow arbitrarily. There is also lexing support for both of these, such that the N suffix on an integer creates a BigInt and the M suffix creates a BigDecimal.

Steps

• Determine if we're implementing these ourselves or bringing in a library
  • Explore libraries and determine best options based on run-time and compile-time performance
  • Add the lib as a submodule and hook it into cmake, if we are adding one
• Add big_integer and big_decimal objects
• Update C API with jank_create_big_integer and jank_create_big_decimal to aid in LLVM IR gen
• Add operator overloads for them (follow ratio)
• Don't worry about all of the math overloads for them for now; those aren't being used with LLVM IR gen right now anyway
• Add lexing support for N and M suffixes, with tests
• Update numeric lexing for integers to automatically use a big_integer if the number is too large for a native_integer, with tests
• Update clojure.core/integer? and runtime::is_integer
• Add clojure.core/bigint, clojure.core/biginteger, clojure.core/bigdec, clojure.core/decimal?
• Update ratio object to use big_integer for its parts