isogram: fix build issues

The test file was trying to import the example code which it shouldn't
do. Also removed unneeded package declarations and renamed the test
file to be consistent.

saddle-points: add to track

rna-transcription: add hint to Ignore annotation

Fixes #420

Base patched Trackler gem off actual version tag.

- was: hand-rolling a version of Trackler based of master and then
  applying changes from the PR/commit/local change to that trackler gem.
- now: using the exact tagged version of Trackler as the basis for the
  hand-rolled gem.

This fixes the issue where a change make to Trackler's master is
incompatible with the current version of x-api.  In short, we were
building the Trackler gem wrong.

nth-prime: simplify example implementation

Secret-handshake: remove whitespace

difference-of-squares: remove whitespace

pascals-triangle: update to v1.0.0 tests

Add script to prune extraneous .keep files

Initial configuration specifies that "first-timers only" issues should
be exempt from cleanup.

palindrome-products: make class use instance methods [Fix #377]

bookstore: fix test suite equality checks

atbash-cipher: make class use instance method [Fix #366]

Fixes issue #377.

Fixes issue #366.

INSTALLATION.md: Fixed spelling errors in documentation

flatten-array: update to v1.1.0 of canonical tests

pig-latin: convert to use instance methods

prime-factors: convert to use instance methods

nth-prime: make use instance method [Fix #358]

https://github.com/exercism/x-common/blob/d7a3c09b6758a8a5d59a2e140e6684031316280a/exercises/flatten-array/canonical-data.json

+ bookstore: add missing import statement in tests

twelve-days: use instance methods [Fix #357]

Beer song instance methods

Fixes issue #357.

Refactoring from static methods to instance methods

sum-of-multiples: use instance method instead of static method [Fix #355]

difference-of-squares: adjust API to use instance method [Fix #253]

Fixes issue #355.

Sieve redundant array