Event for start printing row and cell

[mojtaba-khallash]

Fix #3038

[HackbrettXXX]

Lets discuss my #3038 (comment), before I merge this.

[nielsnl68]

I like this future, the only issue i have with it is that you assume that both rowStart and cellStart are a function.
Please consider changing if (config.rowStart) {...} etc into if (("rowStart" in config) && (typeof config.rowStart ==="function") {...}

[mojtaba-khallash]

I hope @HackbrettXXX accept to merge :)

[HackbrettXXX]

Alright, I'll merge the PR.

• please add the new API to the typings
• We might pass the jsPDF document as second parameter to the callback functions. What do you think?

[HackbrettXXX]

Alright, thanks!