srfi-13: use fx operators
srfi-13: add fast paths for string-prefix? and string-prefix-ci?
srfi-13: use ##sys#substring and core's checkers instead of srfi-13's %substring/shared for string-take[-right] and string-drop[-right]
srfi-13: optimize string-concatenate
srfi-13 tests: add test counter
srfi-13: fast path for string-contains and string-contains-ci
Fast path in C_i_string_ci_equal_p for when the given arguments are equal (==)
srfi-13: fast path for string= and string-ci=
srfi-13: fast paths for string-suffix? and string-suffix-ci?