Add "firstValueLine" and "customValueLine"

[joshuajung]

This is not a bug, just a feature suggestion.

LightChart already comes with the currentValueLine, which draws a horizontal line at the last known value and works great.

I would like to suggest adding two more line types:

• a firstValueLine (showing the first value in the data row)
• one or multiple customValueLines (showing a horizontal line at a value to be defined by the user).

Background: I use LightChart for stock charts. It would be nice to draw a line at the first value of the chart (e.g. the opening price in the morning) or another arbitrary value (e.g. 0 or the closing price of the previous day).

Thanks for considering this! It's not urgent, but I think it would make a nice addition.