Add more geostyler functions

[KaiVolland]

Conversion functions would be handy: toString, toNumber, …

Missing mapbox expressions:

• [ ] step

[jansule]

:tada: This issue has been resolved in version 9.0.0-next.1 :tada:

The release is available on:

• npm package (@next dist-tag)
• GitHub release

Your semantic-release bot :package::rocket:

[jansule]

:tada: This issue has been resolved in version 9.0.0 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot :package::rocket: