doc: tidy.
System::Driver: corrected ErrorCode for Datastore construction failure.
dep: added ceformat dependency; README tidy.

dep/README: wrapping.
dep/.gitignore: added 'ceformat'.

premake_common: added ceformat includedir.
config: added HORD_FMT_SCOPED_* and HORD_THROW_ERROR_F macros.
System::Driver: report root path with non-unique error message.