Add a basic verify setup command
Introduce structure for verification results
Add support for custom verifiers
Add verification for command syntax checkers
Rename :verifier to :verify
Warn about unregistered syntax checkers
Warn if there are no syntax checkers for a buffer
Add binding for flycheck-verify-setup
Document flycheck-verify-setup
[Fix #338] Merge branch '338-verify-setup'

* 338-verify-setup:
  Document flycheck-verify-setup
  Add binding for flycheck-verify-setup
  Warn if there are no syntax checkers for a buffer
  Warn about unregistered syntax checkers
  Rename :verifier to :verify
  Add verification for command syntax checkers
  Add support for custom verifiers
  Introduce structure for verification results
  Add a basic verify setup command
Update changelog and texinfo manual [#338]
Use function quotes in key definitions
Rename :doc-printer to :print-doc

Let's keep a single style
Rebuild texinfo manual