Implemented connection pooling

This is an implementation of connection pooling using the pooler library. With it, I can see significant performance improvements (almost 2 times when repeatedly calling `DB-GET-INFO`):

Without pooling:

```
CL-USER> (time (loop repeat 1000 do (clouchdb:get-db-info)))
Evaluation took:
  1.006 seconds of real time
  0.542259 seconds of total run time (0.389484 user, 0.152775 system)
  [ Run times consist of 0.020 seconds GC time, and 0.523 seconds non-GC time. ]
  53.88% CPU
  9 lambdas converted
  3,417,932,134 processor cycles
  51,915,248 bytes consed

With pooling:

CL-USER> (time (loop repeat 1000 do (clouchdb:get-db-info)))
Evaluation took:
  0.638 seconds of real time
  0.272336 seconds of total run time (0.269197 user, 0.003139 system)
  [ Run times consist of 0.014 seconds GC time, and 0.259 seconds non-GC time. ]
  42.63% CPU
  9 lambdas converted
  2,168,152,634 processor cycles
  35,628,176 bytes consed
```