Fixed Input command to accept and evaluate an expression using getln()

[Megamemnon]

added global variable static unsigned char *tmptxtpos; added local variable int value (in input: closure); added inputagain: identifier and repeatable code to populate identified variable with value entered via getln();this also supports the use of variables in expressions entered in response to the Input command which is kinda cool.

[BleuLlama]

Thanks!