better output for cell magics

[Josverl]

normal cells show the eval of the last (non-blank) line
(its complicated to do so , but it allows for simple use)

the %%micropython cell magic does not do this

# %%micropython
msg = "Hello World"
msg

implementation option :

• take the last line
• check if we can eval that in Cpython ( or use the ipython methods for that ?)
• ( if syntax error ) then execute the entire cell as normal ( not beatiful, but effective )
• otherwise
  • remove the last line
  • run the first part of the cell ( if any)
  • eval the last line : mpremote resume eval "msg"
    combine the results