change/add some log messages
rename some constants and varibles, add the type of cache entry and fix the delete and insert queries
refactor the handler methods, get cache type dynamically and add select query
use the cf pool instead of ngx_cycle pool, this was causing a memory conflict with the sqlite memory allocation
refactor purge location to give feedback about purge operation
add methods to handle with btrees and cache zones, and implement the cache purge from memory and disk