Add cross-referencing comments r.e. stripping ignores

Rename sut variable [Fix #621 #622 #623 #624]

journey test: pull in improvements from xkotlin

https://stackoverflow.com/questions/21612980/why-is-usr-bin-env-bash-superior-to-bin-bash

https://stackoverflow.com/questions/21612980/why-is-usr-bin-env-bash-superior-to-bin-bash

This makes it easier to compare the xjava and xkotlin Travis
configuration files.

Reference: https://stackoverflow.com/a/11651184/2911458

Parallelize unit tests

Delete ignored key from config.json

Since the exercise implementations are all in the exercises directory
we no longer need to ignore any non-exercise directories in the root
of the track.

Normalize format of config file

 This will let us script changes to it with less noise in the diffs.

See https://github.com/exercism/xkotlin/pull/61 for context.

isogram: add hint for german umlauts encoding

Rename the global exercise hints file

We've had some difficulty coming up with a good name for the file
that gets included in all of the exercise READMEs for a given track.

These are global hints, like how to run the test suite, which are
relevant to all the exercises on a track.

We started with SETUP.md in the root of the repository, then renamed
that to exercises/TRACK_HINTS.md because SETUP.md was misleading and
confusing, but then we realized that TRACK_HINTS.md was a bit ambiguous
and confusing as well.

Finally we settled on putting the file in the docs directory, since
this is user-facing documentation, and calling the file
EXERCISE_README_INSERT.md

See https://github.com/exercism/meta/issues/5 for context.

collatz-conjecture: update to latest tests

https://github.com/exercism/x-common/blob/c7c078dbe85e03bd90e6eb343e154f2d176175cc/exercises/collatz-conjecture/canonical-data.json

ocr-numbers: estimate difficulty, position

Use Gradle wrapper for CI jobs

word-search: add to track

saddle-points: API cleanup, ordering

clock: set estimated difficulty to 7

book-store: cleanup, estimate difficulty

change: estimate difficulty, update order

https://github.com/exercism/x-common/blob/73f439401051f3e5a14b07dd43f64ca5cd41b405/exercises/saddle-points/canonical-data.json

Order of identified saddle points is not important.

- Swap Bookstore for BookStore;
- Pass basket of books to method rather than constructor (simpler mental
  model);
- Remove redundant Arraylist wrappers.

perfect-numbers: set estimated difficulty to 3

collatz-conjecture: add to track