#97 Add SQRT square root SQL function

[Simon Chenery]

Add SQRT SQL function. For example,

SELECT SQRT(variation) FROM statistics;

SELECT SQRT((X - 10) * (X - 10) + (Y - 20) * (Y - 20)) FROM positions;

An SQLException is thrown if the value if negative.

[Simon Chenery]

See similar Feature Request #93 Add ABS absolute value SQL function.