Rework header file - add names to prototypes and comments

[DictumMortuum]

Your header file is how most people will first see your code and try and understand how to use it. Thus putting the parameter names into the header file is probably a good idea as it helps document their usage.

bool bitmapGet   (byte *, int);
void bitmapSet   (byte *, int);
void bitmapReset (byte *, int);
int  bitmapSearch(byte *, bool, int, int);

Additional the action of bitmapSearch is not obvious thus a comment on its usage in the header would probably be a good idea. Actually a small blurb about how the first parameter can be an array would probably be a good idea (as it is not obvious without reading the code).

[DictumMortuum]

Applies to external sort, too.