#98 Inline parsed literals via ::~

[Kirill Smelkov]

rst: Add support for inline parsed-literals via ::~ postfix

Just like with :: let's have ::~ to start a parsed-literal block, e.g.
like this

A paragraph::~

Alpha *beta* gamma
Q

which is equivalent to

A paragraph:

.. parsed-literal::

Alpha *beta* gamma
Q

P.S. The patch was not thoroughly written, because based on earlier
experience, I suspect the probability of its inclusion is low. Still
imho it's good to have at least as a demo.

[Kirill Smelkov]