Allow user to take the square root of a number

• While generics is not out yet (v < 1.18), this Stack can hold float64 values.
• Push, Pop, Peek, Size, IsEmpty

• Must update go version to 1.18

Command line interface for RPN calculator

• help shows commands
• +, -, /, *, sqrt, ^ as math operations
• peek, pop as stack operations

Write an CLI command option -eval which will:

• Parse the RPN expression
• Compute the result and push into stack

Ex:
gocalc -compute 3 5 + 7 2 – * should evaluate to 40

Calling GUI from terminal should permit expression evaluation as in CLI