Version differences

 The interface for MODRES has changed slightly between versions. The main
 thing to remember, when writing programs that use MODRES, is to check the
 version of the MODRES in memory, and only use the newer options if they are
 available. I've only looked at v2.01 for the new functions, but I think
 they were available as far back as v1.52 - possibly even v1.4.

 The first problem to worry about is the device number. In old versions,
 specific values were assumed to apply to specific devices. In the new
 versions, the available devices are determined from a table that is
 returned by residency test (function 21).

 The next difference is in the ability to handle samples greater than 64K
 in length and to specify the quality of the output. Two bytes were added
 to the table used in the "Play a module" function (20) to do this.

 There were also bytes added to the table used in playing a sample (function
 23). These allow the user to change the volume of the sample, the quality
 of the output, and permit samples to loop. A change was also made to the
 format of the length field to allow samples with lengths greater than 64K
 to be played.

 Other than these changes to the existing structure, the new versions also
 provide two additional functions (24 and 27) which are used to load a MOD
 from disk and play it.

 Please note that this "new" information is entirely theoretical - none of
 these features have been tested.