tweak MyPage docs

/** \class LAMMPS_NS::MyPage

 * \brief Templated class for storing chunks of datums in pages.

 *

 * The chunks are not returnable (i.e. cannot be freed individually).

 * One can only reset and start over.  The purpose of this

 * class is to replace many small memory allocations via malloc() with

 * a few large ones. Since the pages are never freed, they can be

 * re-used without having to re-allocate them.

 * The size of the chunk may vary from call to call, but must be

 * less or equal than the *maxchunk* setting.

 * The chunks are not returnable like with malloc() (i.e. you cannot

 * call free() on them individually).  One can only reset and start over.

 * The purpose of this class is to replace many small memory allocations

 * via malloc() with a few large ones.  Since the pages are never freed,

 * they can be re-used without having to re-allocate them.

 *

 * The settings *maxchunk*, *pagesize*, and *pagedelta* control

 * the memory allocation strategy.  The *maxchunk* value represents