apl_gradebook: Add entry list ptr

Will point to an array of entries. These will probably be sorted
by time created, just to keep it simple. To display different sortings,
we'll likely just create index arrays which represent different
sortings (ascending/descending score, date created, etc.)
apl_gradebook: Add apl_closebook skeleton func

Free gradebook memory & resources.
apl_entry: Combine ENTRY_*_INT/FLOAT symbols

Doesn't matter whether the score or max values are being described,
both share two possible types: float and int
apl_entry: Stack-allocate the entry label

No reason to deal with a bunch of memory allocations for such small
chunks. 64 bytes is a good chunk size, and a power of 2. Shouldn't
leave much wasted space in the heap
apl_entry: Add apl_newentry method

Creates a new gradebook entry with a given label. Starting score/max are
both zero
Add apl_entry sanity test
apl_entry: Add apl_destroyentry function

For gradebook entry cleanup
Merge branch 'entry' into gradebook