* 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
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.
* Improves testing
* Adds karma-sourcemap-loader
* Adds karma-preprocessor-rollup
* Moves testing Rollup building to Karma
* Enables sourcemaps in tests
* Fixes#2051
* Updating tests to reflect discrepancies with Phantom@^2
* Trying karma-coverage-istanbul-reporter
* Still not working...
* chore: make coverage report of src files
* test: add c3.css
* fix: fix test case of mouse events
* chore: update codecov module
* Adds codecov.yml to ignore polyfill.js
* chore: exclude src/polyfill.js at istanbul layer
* chore: remove rollup-plugin-istanbul dep because not used