fmt: replace Conv record with struct Conv
fmt: replace parse_* structural records with struct Parsed<T>
fmt: simplify parse_type
fmt: simplify parse_flags
fmt: simplify parse_count
fmt: simplify parse_precision
fmt: simplify parse_parameter
fmt: simplify parse_conversion
fmt: simplify parse_fmt_string
fmt: fix formatting and style
fmt: derive Eq for all types
fmt: add unit tests
Merge pull request #4372 from apasel422/fmt2

Modernize core::extfmt::ct