Step process made prettier about sos

[BoPeng]

Liked the new syntax a lot so I implemented it. We can revert the changes if it does not work out.

[gaow]

Indeed it is prettier. Will test it out and raise problems if there is any!

[BoPeng]

It is a parser trick to convert

action: option
   text

to

process: option
action('''text''')

with automatic dedent of text. The difficult part was we might see things like else: in python code but it should work now after I disallow all Python keyword as action names.