* Avoids boot time mutation of REGISTER constant
* Allows to define project specific expression parsing
* Avoids custom (slow) serialization of Expression objects speeding up
reporter / killer IPC
* Improve specification
* Improve integration API as it now finally references an object the config
* Allow reproduction of syntax from Expression#syntax
* Allow instantiation of Expresssion objects without generating the
syntax, much nicer for most specs & internal code, avoids generating
a string to parse it into an expression
* Fix LSP violation in Mutant::Matcher namespace
* Do not mix concerns of domain with building an object graph concerning
the domains execution environment
* Removes the amount of clutter in Env (mostly a cleanup for tracing
where Env will grow a bit)
* The SCOPE_PATERN constraints `namespace` to be characters that are
valid literal static regexp.
* Not test case can be created that forces Regexp.escape here.
