Add AEAD_AES_128_GCM SRTP Profiles

Relates to pion/srtp#85

Fix flight1 handshakeRecvSequence handling

Only update handshakeRecvSequence when the flight successfully
completes. Before we would prematurely increment putting us in
a state where it would never complete.

Resolves pion#263 pion#262

Release 2.0.0

Fix connCtx.RemoteAddr()

LocalAddr of the underlying conn was returned from RemoteAddr.
Add TestLocalAddrAndRemoteAddr.

Fix listen example error handling

Don't call hub.Register if Accept returned error.

v2.0.0-rc.8

Since rc.7 the following changes have been made:

* CCM is no longer part of the default cipher suites pion#201
* SNI extension support pion#194
* End to end tests with OpenSSL client/server pion#193
* Large refactor of the handshake using the state machine from RFC6347 Section 4.2.4 pion#208
* Fixes for a number of deadlocks
* Replay attack protection pion#215
* Verify the protocol version pion#211
* Fix the hash algorithm detection pion#224
* Close the connection on a sequence number overflow pion#214
* Concurrent read and accept pion#226
* Insecure hash algorithms are disabled by default pion#231

Prefer GCM over CBC suites

Match OpenSSL (and Chromium's) ordering of CipherSuites.
Go also has a hardware accelerated implementation, so this should
be a better experience in almost all cases.

Relates to pion#199

v2.0.0-rc.6

* Key is verified before cipher suite initialisation
* Expose SelfSign helper and the CCM package
* Make HashAlgorithm private
* Listener is now compatible with stlib net.Listener
* Conn is now compatible with stdlib net.Conn
* New top-level functions CipherSuiteName, CipherSuites
  and InsecureCipherSuites added to match upcoming
  additions to crypto/tls in Go 1.14
* Added support for using context.Context for cancellation
  in Dial, Client and Server

v2.0.0-rc.6

* Key is verified before cipher suite initialisation
* Expose SelfSign helper and the CCM package
* Make HashAlgorithm private
* Listener is now compatible with stlib net.Listener
* Conn is now compatible with stdlib net.Conn
* New top-level functions CipherSuiteName, CipherSuites
  and InsecureCipherSuites added to match upcoming
  additions to crypto/tls in Go 1.14
* Added support for using context.Context for cancellation
  in Dial, Client and Server

Check err before/after calling Read

Read should be refactored so that we can get rid of storing
readErr entirely, but for now this is good