missing proxy docs

[dormando]

importing some TODO's/missing sections that are getting trimmed via a PR:

- `resp:code()`: the response code. Common codes are:
  - `mcp.MCMC_CODE_OK`
  - `mcp.MCMC_CODE_STORED`
  - `mcp.MCMC_CODE_EXISTS`
  - `mcp.MCMC_CODE_MISS`
  -  TODO: document the rest.

from examples page:

### Cache Layering Cons
- Needs more complex application clients.

- Configuration of pools needs to be managed in two places (application
  clients, memcached proxies)

---

# Use Case Examples

## Simplifying and Unifying Cache Clients

## Distributing data by usage

## Best effort data redundancy

## Transparent upgrades

## Transparent pool resizing

## Protocol translation

[dormando]

Other missing sections:

• what a pool does needs a lot of expansion. This is and always has been the number 1 most confusing aspect of memcached, because of the direct hash map approach.
• deeper explanation of the pool options (ketama/etc emulation for converting existing pools)
• how config reload works (doesn't drop in-flight requests, allows rewriting the code live, etc)
• API: cron code

[dormando]

the inspector and mutator objects are also missing docs.

logging API calls not well documented or missing. stats counters missing.

[dormando]

could use a summary page listing what you can do with the proxy.

need to do another pass on the old wiki.. lots of random "wisdom" pages got dropped.

[dormando]

need a page on how error/down servers are handled in various scenarios. (ie; antiflap, combined with failover_route, etc).

should demo a timeout failover route thingie too