Project 5 - Game v0.8

project_5.html
Add onkeyup event handler to input txtCommand. This calls function
setBtnTxtCommand to check whether txtCommand is blank and set status of
btnTxtCommand accordingly.
Now that btnTxtCommand is active only when field is not blank, bypass
the verifyTxtPresent function and go directly to function
simpleTextCommand.
Function verifyTxtPresent is still used by txtCommand onkeypress event
when Enter key pressed; if text is present we proceed to function
simpleTxtCommand.

project_5_main.js
Move a few sections around and update comments for clarity.
Add function setBtnTxtCommand to check whether txtCommand is blank and
set status of btnTxtCommand accordingly.
Function verifyTxtPresent is still used by txtCommand onkeypress event
when Enter key pressed; if text is present we proceed to function
simpleTxtCommand.