Implement MKn$, CVn serialization functions

[ngeor]

MKI$, MKL$, MKSS$ and, MKD$ convert numbers to numeric strings that can be stored in FIELD statement string variables. CVI, CVL, CVS, and CVD convert those strings back to numbers.

MKI$(integer-expression%)
MKL$(long-integer-expression&)
MKS$(single-precision-expression!)
MKD$(double-precision-expression#)
CVI(2-byte-numeric-string)
CVL(4-byte-numeric-string)
CVS(4-byte-numeric-string)
CVD(8-byte-numeric-string)

Hint:

PRINT MKI$(33 + 256 * 34)

prints !" (33 is the ascii code of ! and 34 is the ascii code of ")