This commit refactors the test suite to make it cleaner and to use the
standard testing library better. The `assert()`, `equals()`, and `ok()`
functions have been removed and some test names have been changed for
clarity.
No functionality has been changed.
This commit adds a cache to the freelist which combines the available free pages and pending free pages in
a single map. This was added to improve performance where freelist.isFree() was consuming 70% of CPU time
for large freelists.
This commit fixes the freelist so that it frees from the beginning of the data file
instead of the end. It also adds a fast path for pages which can be allocated from
the first free pages and it includes read transaction stats.
I changed the Transaction/RWTransaction types to Tx/RWTx, respectively. This makes the naming
more consistent with other packages such as database/sql. The txnid is changed to txid as well.