rule_engine: Readability updates.
rules.c: Rename id checking function to match what it's checking.
tc_regression: Fixing unit/clipp unit test.
predicate: Change null to [] in grammar. RNS-661
predicate/parse.cpp: Refactor in preparation for named literals. RNS-661
predicate: Add support for named literals. RNS-661
predicate/parse: Refactor and expose parse_literal_value(). RNS-661
predicate: Initial conversion back to Value based nodes instead of ValueList.  See below.  RNS-661

Standard and the module have not been converted yet, so this commit currently fails to build.
lua/ironbee/predicate.lua: Remove streq and istreq references.
predicate/call_helpers: Update to use Value instead of ValueList. RNS-661
predicate: Node::eval_initialize() now takes a GraphEvalState instead of a NodeEvalState.
predicate/Makefile.am: Split into libpredicate.la and libpredicate_standard.la.
predicate/dag.hpp: Add Literal(Value) constructor.
ironbee/field.h: Minor documentation cleanup.
predicate/eval: Change NodeEvalState::add_to_list() to append_to_list().
ironbeepp/field.cpp: Field::to_s() now always includes decimal point for floats.
predicate/value: Create a Value class to provide easier use of Value's. (See below)

While a Value is a ConstField in a strong sense, it has several restriction on Fields and a few extra features.
predicate: NodeEvalState::setup_local_list() now takes a MemoryManager instead of an EvalContext.
predicate/eval: Add NodeEvalState::setup_local_list() version that takes a name.
predicate/dag.hpp: Fix documentation error.