use `fmatch` when matching patterns

correct behavior of `--modulestd` -- actually replace the system include

add `--modules`, `--modulestd` and `--modulestdcompat` to allow using `std` module and set module mapping

convert `#include<>` to modules

convert `#include<>` to modules

add `--outextmod` and `--outextmodimpl` arguments * `--outextmod` output module interface unit file extensions. default: .cppm * `--outextmodimpl`: output module implementation unit file extensions. default: .cpp

add `--inextheader`/`--inextcxx` to readme

add `--inextheader` and `--inextcxx` * ` --inextheader`: input header file extensions * `--inextcxx`: input C++ source file extensions

minor: __str__() to allow enum to look nicer