flow 0.2.0

• The LICENSE was switched from GPL-3 to MIT
• New function: flow_compare_runs() displays 2 calls on the same diagram, making it easy to
  observe their divergence
• New function: flow_view_uses() displays functions that recursively call its input, basically it
  does the opposite of flow_view_deps()
• New function: flow_view_source_calls() draws the dependencies between files sourcing each other.
• flow_view_deps() gains an include_formals arg, TRUE by default, so it
  displays dependencies used in formals.
• flow_view_deps() accepts a list of functions as input, to display a diagram
  that starts from several functions.
• flow_view_deps()'s trim, promote, demote, trim arguments support
  regular expressions.
• flow_view_doc() and flow_view_doc() were simplified to output only html since
  the md output was rarely used and brittle.
• flow_debugonce() is deprecated, use flow_debug() and flow_undebug()
• Diagram drawing functions now return by default a "flow_diagram" object, it
  contains the widget, the code and the data of the diagram and has a print()
  method that displays the diagram.
• Bug fixes