Add pkger source driver support (golang-migrate#377)

* Add pkger source driver support

As go-bindata has been abandoned [1] there are open requests, golang-migrate#116, for
alternative sources with similar functionality. The Buffalo project [2]
created packr and recently pkger [3] was announced [4] with the
intention to supersede packr.

This change adds support for using pkger as a source.

The implementation relies on httpfs.PartialDriver for pretty much all
functionality.

[1] jteeuwen/go-bindata#5
[2] https://gobuffalo.io/
[3] https://github.com/markbates/pkger
[4] https://blog.gobuffalo.io/introducing-pkger-static-file-embedding-in-go-1ce76dc79c65

* pkger: rename Instance to Pkger

* pkger: make WithInstance accept *Pkger

* pkger: refactor and add access to global pkging.Pkger instance

* pkger: fix typo and cleanup debug logging

Merge pull request golang-migrate#356 from jace-ys/master

Move migrate binary to /usr/local/bin in Dockerfile

Actually release windows 386 build

Merge pull request golang-migrate#343 from martinlindhe/win386

build-cli: Also build GOOS=windows GOARCH=386, fixes golang-migrate#339

Use new ql driver location

Merge pull request golang-migrate#305 from bxcodec/fixClickHouse

hotfix(dependency): resolve clickhouse dependency breaking changes

Add official support for firebird back

Improve error message in case no migration is found (golang-migrate#158)

* Improve error message in case no migration is found

* Return similar error

* Just log the error

* Fix error message

Properly filter out custom query params in MySQL DB driver

Addresses: golang-migrate#272

Let database.Open() use schemeFromURL as well (golang-migrate#271)

* Let database.Open() use schemeFromURL as well

Otherwise it will fail on MySQL DSNs.

Moved schemeFromURL into the database package. Also removed databaseSchemeFromURL
and sourceSchemeFromURL as they were just calling schemeFromURL.

Fixes golang-migrate#265 (comment)

* Moved url functions into internal/url

Also merged the test cases.

* Add some database tests to improve coverage

* Fix suggestions