AddHandler refactoring

* remove unneeded check for adding more handlers
* rename Set->AddHandler
* check for handlers on lookupd connect
* panic on already connected to nsqd/nsqlookupd
Merge pull request #48 from jehiah/concurrent_handlers_48

separate handlers for concurrent handlers
negotiate V1 response
remove deprecated codepath
changelog/migration guide
Merge pull request #57 from mreiferson/changelog_57

0.3.7 to 1.0.0-alpha migration docs
make note of UPGRADING in README
Change to local 'rng' instead of global 'rng'

Fixes #61
test against a matrix of nsqd versions
Merge pull request #60 from mreiferson/deprecated_60

clean up some deprecated items
Merge pull request #25 from mreiferson/matrixxxx_25

test against matrix of nsqd versions
make consumer lookupd_http_address handling work like pynsq

would fail if scheme was present, but path was completely blank (not even just /)
Merge pull request #63 from ploxiln/lookupd_address_no_path_63

handle lookupd_http_address like pynsq
producer: fix write IOError deadlock

if `WriteCommand` fails, since it only occurs inside the same goroutine
that receives `Delegate` events, the call to `WriteCommand` deadlocks
trying to delegate the `IOError` (which sends to `Producer.ioErrorChan`)

fix it by just closing inline
Merge pull request #65 from mreiferson/producer_deadlock_65

producer: fix write error deadlock
Fix typo.
Merge pull request #68 from fuseelements/fix/doc

Fix typo.