update mysql querier to use a single pool

now spins connections off of a single pool on each
instance of mysql querier

this is done to allow good error handling in future updates

the way mysqlquerier is called will be much different.
rename mysql-querier

will be using index as top-level instead
add index

top-level handler for mysql-querier
rename index to mysql-querier
update test to work with new querier
rename test to example
change mysql-querier to singleton pattern

this allows mysql-querier to be ended at the top-level
since one instance is shared

before this change, new instances of mysql-querier were created
at each call to require().  thus, mysql-querier needed to be
deleted at the end of each use, which is not the desired behaviour.

no change to depending classes is necessary.
update category stream to use new mysql-querier
update category import to work with new mysql-querier
add test for category stream
update boardstream to work with new mysql-querier
update boardstream test to work with new implementation
end mysql-querier in index
handle eror on import-categories
update import-boards to work with new mysql-querier
update userstream to use new mysql-querier
update test userstream
update import-users to work with new implementation
update threadstream to use new mysql-querier
update test threadstream to work with new impelementation