chore(*): add PR template, add TSDoc comments

src/types/LintRule.ts

@@ -1,6 +1,10 @@
 import { Diagnostic } from './Diagnostic'
 import { LintRuleType } from './LintRuleType'
 
+/**
+ * A lint rule is defined by a type, name, description, warning text and a test function.
+ * The test function produces a set of diagnostics when executed.
+ */
 export interface LintRule {
   type: LintRuleType
   name: string
@@ -9,10 +13,16 @@ export interface LintRule {
   test: (value: string, lineNumber: number) => Diagnostic[]
 }
 
+/**
+ * A LineLintRule is run once per line of text.
+ */
 export interface LineLintRule extends LintRule {
   type: LintRuleType.Line
 }
 
+/**
+ * A FileLintRule is run once per file.
+ */
 export interface FileLintRule extends LintRule {
   type: LintRuleType.File
   test: (value: string) => Diagnostic[]