Stability fixes

- left client timers active when destroying client, leading to invalid
  memory access within zloop (crash).

- did not free zlog per server, leading to memory leakage.
Fixed issue in BNF grammar

- for dictionary items was not flagging longstr as used
- so some protocols (FILEMQ) had missing terms in them
Added CZMQ_EXPORTs for Win32
Added log and config to server_t

- lets application do logging
- lets application access loaded config data
Ensure client IDs are always unique

- when starting multiple server instances, each would start with ID 1
- this made it impossible to distinguish different clients
- now each server starts at random ID (0..1000)
Merge pull request #45 from hintjens/master

Stability fixes and other changes