chore(docs): revise makeExcerpt mixin for DRYer ref to examples

[chalin]

Avoiding ts in the file path will make it a bit easier to construct the path to the Dart version (by simply appending to the path rather than having to massage the path).

This update allows us to be more DRY when referencing examples and excerpts. E.g.,

+makeExample('quickstart/ts/app/app.component.ts', '', 'app/app.component.ts')
+makeExample('quickstart/ts/app/app.component.ts', 'import', 'app/app.component.ts (import)')(format='.')

can now be just

+makeProjExample('app/app.component.ts')        // NOTE the new mixin name
+makeExcerpt('app/app.component.ts', 'import')  // NOTE the new mixin name

With the resulting examples and their titles being rendered the same as before. The original makeExample has been left untouched.

Applied new mixins to quickstart.

[chalin]

@kwalrath, @wardbell : can you have a look?

[kwalrath]

LGTM. @wardbell do you have an opinion? I wonder if the name makeExample1 could be clearer. makeExample2? makeSimpleExample?

[Foxandxss]

Or perhaps makeLocalExample? I personally don't like example1, example2 kind of names because you can easily forget which is which.

[wardbell]

I like but the name has to change. makeLocalExample isn't bad. Or makeProjectExample. Either works for me ... anything except example1.

Happy to accept after that change.

[chalin]

I agree about the name, but figured I run by the basic idea first.

I originally thought of: makeEg as a short name (to represent that is takes the short argument list).
Otherwise, makeProjExample? (I'm trying to keep the name reasonably short.)

[chalin]

Then makeProjExample it is.
@kwalrath @wardbell : ready to merge.

[kwalrath]

OK, I'll merge a little later this morning. Thanks, Patrice!