Some basic evaluation support for square roots over ``:num`` and ``:real``. Also add syntax support for transcTheory.

Tidied up logrootScript.sml. The evaluation theorems for ``ROOT 2`` were present but they weren't being used.

Over the reals a conversion is used -- this will only work for rationals built from perfect squares. For example:

> EVAL ``sqrt (9 / 16)``
val it = |- sqrt (9 / 16) = 3 / 4: thm