Make Colons exemptable through a project Vocab

Amends the previous commit, which claimed the proper-noun exemption
couldn't be expressed. It can — Vale applies Vocab accept.txt entries as
exceptions to any check, not only Vale.Spelling and Vale.Terms.

Two things stopped it working here:

  - the token matched ': C', so the matched text was never the proper
    noun and there was nothing for the vocabulary to compare against
  - `nonword: true` opts out of vocabulary matching altogether

Matching the word itself via a lookbehind, and dropping `nonword`, makes
`accept.txt` work exactly as reported in issue #20: with Kubernetes in a
project vocabulary, "You need one thing: Kubernetes." is now silent while
"... : Terraform." still flags.

The notice-label exemptions move into the lookbehind so they still apply
now that the match starts at the word. Alerts also read better:
"'Concise' should be in lowercase" rather than "': C'".

Author: jdkato

Google/Colons.yml

@@ -1,12 +1,13 @@
 extends: existence
 message: "'%s' should be in lowercase."
 link: 'https://developers.google.com/style/colons'
-nonword: true
 level: warning
 scope: sentence
-# The guide exempts text after a notice label ('Caution: Deleting this is
-# permanent.'), so the four label types are excluded here. It also exempts
-# proper nouns and quotes, which this check can't detect — `existence` has no
-# exceptions field. See issue #20.
+# The match is the word itself, not ': X', and `nonword` is off. Both are
+# required for a project Vocab to work: Vale compares accept.txt entries
+# against the matched text, and `nonword: true` opts out of that entirely.
+# So a proper noun after a colon can be exempted by adding it to accept.txt.
+# The guide's other exemption, notice labels, is handled by the lookbehinds;
+# headings are already excluded by `scope: sentence`. See issue #20.
 tokens:
-  - '(?<!:[^ ]+?)(?<!Note)(?<!Caution)(?<!Warning)(?<!Success):\s[A-Z]'
+  - '(?<!Note: )(?<!Caution: )(?<!Warning: )(?<!Success: )(?<=:\s)[A-Z]\w+'

testdata/Punctuation.ct

@@ -3,7 +3,7 @@ $ vale --output=line --sort --normalize --relative --no-global --no-exit .
 test.md:3:5:Google.Periods:Don't use periods with acronyms or initialisms such as 'N.B.A.'.
 test.md:5:18:Google.OptionalPlurals:Don't use plurals in parentheses such as in 'key(s)'.
 test.md:5:21:Google.Parens:Use parentheses judiciously.
-test.md:7:5:Google.Colons:': C' should be in lowercase.
+test.md:7:7:Google.Colons:'Concise' should be in lowercase.
 test.md:9:40:Google.OxfordComma:Use the Oxford comma in ', Rand and God.'.
 test.md:11:46:Google.EmDash:Don't put a space before or after a dash.
 test.md:13:24:Google.EmDash:Don't put a space before or after a dash.
@@ -23,4 +23,4 @@ test.md:41:17:Google.OxfordComma:Use the Oxford comma in ', green and orange.'.
 test.md:45:31:Google.OxfordComma:Use the Oxford comma in ', an external drive or OneDrive.'.
 test.md:51:6:Google.Parens:Use parentheses judiciously.
 test.md:51:21:Google.Parens:Use parentheses judiciously.
-test.md:57:18:Google.Colons:': A' should be in lowercase.
+test.md:57:20:Google.Colons:'Apples' should be in lowercase.