- Update cmake parameters

- Update to version 4.5.0+git.20170523:
* update readme
* ignore Z3-str source
* failing test case: SMT2 parse string constants
* create and register string theory plugin the parser gets a little bit further now! rejects input with "unexpected character"
* fix string constant representation in parser spec1 loopback OK
* pretty-printing of string constants in AST spec2 looks good now
* load str decl plugin; recognize String sorted constants
* register Concat function now reaches str_decl_plugin::mk_func_decl()
* at least for now, Concat is no longer associative this means that we'll always have (Concat a b) instead of variadic forms
* add Length function to theory of strings
* AND MUCH MORE...