Custom variable names

[gavinmcfarland]

It would be useful to introduce a way for users to choose custom variables names when the source code is generated.

One suggestion is to add a label to the layer name using a specific syntax:

Layer Name <customNamedFrame>

This would be extrapolated to:

var customNamedFrame = figma.createFrame()
customNamedFrame.name = "Layer Name"

Need to consider the syntax for this so it doesn't conflict with other plugins and has the potential for future features.