system: added file & directory creation & removal.

system:
	added create_file() and remove_file();
	added create_directory() and remove_directory().
test/system/general: added file & directory creation & removal tests.
kvs: added info-less read(), read_file(), and write_file().
test/kvs/echo: simplified.
resource_manager: corrected register_handler() error message; tidy.
impl/system/linux: ignore ENOENT in is_X() stat; tidy.
impl/system/linux: tidy.
filesystem: new module sliced from system.
test/system/general: removed filesystem module tests.
test/filesystem/general: new test (sliced from system_general).
filesystem: added WorkingDirScope.
filesystem: moved path NUL-termination notes to .dox.
filesystem: #include tidy.
tool_build: new tool (stub).

premake:
	made togo outdir explicit;
	added make_tool();
	added stub project for tool_build;
	added exclusions for tool_build.

togo.sublime-project:
	added `Source: tool_build` folder;
	added exclusions for tool_build.