remove config package-scoped variables

[crandles]

As part of supporting config reloading (#12), this PR aims to remove package-scoped global variables that are utilized throughout trickster. These are generally hard to maintain if they require post-init updates, and would all require some sort of locking or atomic operations for coordinating usage.

This will not attempt to add config reloading functionality, but should prepare the codebase for it 🤞.

https://peter.bourgon.org/blog/2017/06/09/theory-of-modern-go.html
https://dave.cheney.net/2017/06/11/go-without-package-scoped-variables

TO DO:

• Remove log singleton
• Remove global state required for binding flags
• fix tests
• remove comments

Test failures don't seem to be returned through travis; I may look at that as well.

[jranson]

re: the test failures, if I had just one guess, the cause of the always 'good' test return code is likely because the make test is being piped to a grep that strips log line entries from the output (such that only test results are printed). I would guess that the grep returns exit code 0 even if the make test returns a nonzero exit code, so we may need to pull that out. We could consider another option like setting the logger to be file-based and pointed at /dev/null, instead of console, for tests (it would be a lot of tests to update though!)

[crandles]

this fails for me; there is a default that gets added by the Loader. I think this fails on next too.

[jranson]

@crandles We've merged next into master, so I rebased your PR target here and next is no more. Currently all tests are passing on the master, so if you can rebase locally and fix up any compile failures as a result of the obscene amount of changes, it should be good to go. This is looking really good, thanks! Also, the fix is in for unit tests output and exit code working like it should, while also excluding generated code from the coverage report. I accomplished this by moving the exclusion sed from the Makefile target to the .travisci configuration, so you should be able to see all of the things now locally and in travis. Sorry for the frustrations with that!