Upgrade to Pygments 2.2.0

- Added lexers:

  * AMPL
  * TypoScript (#1173)
  * Varnish config (PR#554)
  * Clean (PR#503)
  * WDiff (PR#513)
  * Flatline (PR#551)
  * Silver (PR#537)
  * HSAIL (PR#518)
  * JSGF (PR#546)
  * NCAR command language (PR#536)
  * Extempore (PR#530)
  * Cap'n Proto (PR#595)
  * Whiley (PR#573)
  * Monte (PR#592)
  * Crystal (PR#576)
  * Snowball (PR#589)
  * CapDL (PR#579)
  * NuSMV (PR#564)
  * SAS, Stata (PR#593)

- Added the ability to load lexer and formatter classes directly from files
  with the `-x` command line option and the `lexers.load_lexer_from_file()`
  and `formatters.load_formatter_from_file()` functions. (PR#559)

- Added `lexers.find_lexer_class_by_name()`. (#1203)

- Added new token types and lexing for magic methods and variables in Python
  and PHP.

- Added a new token type for string affixes and lexing for them in Python, C++
  and Postgresql lexers.

- Added a new token type for heredoc (and similar) string delimiters and
  lexing for them in C++, Perl, PHP, Postgresql and Ruby lexers.

- Styles can now define colors with ANSI colors for use in the 256-color
  terminal formatter. (PR#531)

- Improved the CSS lexer. (#1083, #1130)

- Added "Rainbow Dash" style. (PR#623)

- Delay loading `pkg_resources`, which takes a long while to import. (PR#690)