* Refactors circular dependencies
- Adds src/chart-internal.js
- doesn't need to pass c3.js as argument to rollup
- don't commit c3.js nor c3.min.js
- formatting rollup.config.js
- keep util.js format
- remove unused imports from axis, core and util
* adds more tests for axis and zoom
* restores the way in which chart-internal calls d3 #2060
* fixes linter warnings on axis-spec
Not sure, maybe not related, but at least not synchronized with info in package.json.
I'm haiving troubles with fetching c3 0.4.11 and it tells me:
```
$ bower install
bower c3#0.4.11 not-cached https://github.com/masayuki0812/c3.git#0.4.11
bower c3#0.4.11 resolve https://github.com/masayuki0812/c3.git#0.4.11
bower c3#0.4.11 checkout 0.4.11
TypeError: LRU: key must be a string or number. Almost certainly a bug! undefined
at typeCheckKey (C:\Users\andrii.lundiak\AppData\Roaming\npm\node_modules\bower\node_modules\lru-cache\lib\lru-cache.js:20:19)
at LRUCache.get (C:\Users\andrii.lundiak\AppData\Roaming\npm\node_modules\bower\node_modules\lru-cache\lib\lru-cache.js:230:3)
at C:\Users\andrii.lundiak\AppData\Roaming\npm\node_modules\bower\lib\core\resolvers\GitRemoteResolver.js:122:70
at _fulfilled (C:\Users\andrii.lundiak\AppData\Roaming\npm\node_modules\bower\node_modules\q\q.js:854:54)
at self.promiseDispatch.done (C:\Users\andrii.lundiak\AppData\Roaming\npm\node_modules\bower\node_modules\q\q.js:883:30)
at Promise.promise.promiseDispatch (C:\Users\andrii.lundiak\AppData\Roaming\npm\node_modules\bower\node_modules\q\q.js:816:13)
at C:\Users\andrii.lundiak\AppData\Roaming\npm\node_modules\bower\node_modules\q\q.js:877:14
at runSingle (C:\Users\andrii.lundiak\AppData\Roaming\npm\node_modules\bower\node_modules\q\q.js:137:13)
at flush (C:\Users\andrii.lundiak\AppData\Roaming\npm\node_modules\bower\node_modules\q\q.js:125:13)
at _combinedTickCallback (internal/process/next_tick.js:73:7)
bower c3#0.4.11 resolved https://github.com/masayuki0812/c3.git#0.4.11
bower c3#0.4.11 install c3#0.4.11
```
And I thought, it might be related....
cleared unused commented test case and cleared up spelling errors.
#2251 fixed testcase and somehow removed return statement.
#2251 x-axis tick format is no longer truncated for negative values.
#2251 x-axis tick format is no longer truncated for negative values.