Allow value label on the flow (selectively)

[radeksvarz]

Currently the generated sankey does not present flow values.

However for graphs, where nodes have both more ouflows and inflows it is important to visualise flow value selectively.

Proposal declaration implementation:

Income [100] Budget
renders without flow value label, i.e. as is now

Income [!100] Budget renders with flow value label on the Income side of the flow

Income [100!] Budget renders with flow value label on the Budget side of the flow

Income [!100!] Budget renders with flow value label centered on the flow