Ensures `square root` result is always a string.

Ririsu works with strings all the way down, so we should make sure that all
operations on numbers give us back a string, so that the next operation can
actually work with it.
Ensures arguments to `round` are treated properly.

As the stack always contains strings, functions dealing with number have to
convert between data types properly.
Rounds all numbers.

This is necessary for `integer_to_list/list_to_integer` conversions to work,
which sadly means we need to get rid of the round operation.
Includes the POWER operator for checking sqrt.

This allows us to fix the 100-doors example."
Fixes the 'read' method, which shouldn't execute anything
Fixes hello world example.
Added tag 0.2.0 for changeset 7bd3e385b30c
Bumps version.
Added tag 0.2.0 for changeset ddf9bc819659