policy: Add policy CMP0053

This policy switches between the old EVIS parser and the new, faster
parser.
tests: Add tests for syntax corner cases and CMP0053

Includes tests for:

  - @ expansion during normal execution
  - various characters in variable names for comparison between the new
    and the old parser
  - corner cases in the parsers
  - correct messages when behavior is different
EVIS: Reimplement using custom parsing code

Testing the configure (no generate) step with ParaView shows ~20%
performance improvement.

In terms of complete configure/generate steps, further testing with
ParaView shows a 20% performance improvement over 2.8.12.2 with Unix
Makefiles and minimal with Ninja. Ninja is less because it generate step
is the expensive part (future work will address this) by a long shot and
these changes help the configure step for the most part.
Utilities/Release: Use ${VAR} instead of @VAR@ syntax

The Utilities/Release/Cygwin/CMakeLists.txt is processed in the project,
not configured, so we should avoid using @-replacement syntax.
Windows: Avoid () in environment names

Use a redirection.
Help: Add more reference targets to cmake-language.7
Help: Add documentation on escaping changes with CMP0053
Merge branch 'dev/faster-evis' into next

* dev/faster-evis:
  Help: Add documentation on escaping changes with CMP0053
  Help: Add more reference targets to cmake-language.7
  Windows: Avoid () in environment names
  Utilities/Release: Use ${VAR} instead of @VAR@ syntax
  EVIS: Reimplement using custom parsing code
  tests: Add tests for syntax corner cases and CMP0053
  policy: Add policy CMP0053