Note: there was a breaking change that we forgot to document. Ww write the breaking change here for it to be picked up in the future 3.0 release,
even though it was introduced in commit 3871765
BREAKING CHANGE: the CLI no longer accepts "extra options". Instead you should pass the `-c` flag. To update:
before:
```
showdown makehtml -i foo.md -o bar.html --strikethrough --emoji
```
after:
```
showdown makehtml -i foo.md -o bar.html -c strikethrough -c emoji
```
Closes#916
The CLI was completely rewrote. Changed dependency from yargs to commanderjs,
which is cleaner, faster and has no dependencies.
Also added a complete testsuite for the cli.
Closes#893, #894
