string2path 0.1.0

Breaking changes

• Drop support for R < 4.1.

• Now all functions accept font family name. This is to support TTC file
  properly, which contains more than one fonts. A new function dump_fontdb()
  is useful to check the actual family name (and the weight and the style) to
  specify.
  They also accept a file path, so the existing code should work, except when
  specifying tolerance without the named argument.

• The minimum supported Rust version is bumped to 1.56.0 for the 2021 edition.