Walk's max-repetitions & non-repeaters can be set

* The walk function uses default values.  It's now possible to
change/override the default values via instance variables on
GoSNMP. Closes issue #17 on soniah/gosnmp.
Normalize rootOid. Support for Oids with and without initial dot
Merge pull request #18 from codedance/issue-17-walk-config

Walk's max-repetitions & non-repeaters can be set
Merge pull request #19 from eferro/master

Normalize rootOid. Support for Oids with and without initial dot
removed duplicate method call
Merge pull request #21 from msfe/master

removed duplicate method call for oidToString
Redefined OctetString type as []byte

OctetStrings were being incorrectly based to a Go string.  SNMP
OctetStrings contain binary data.  In many cases they are strings but in
other cases they are binary data such as values containing bit flags.
Casting the data to a string will lead to loss of information (e.g.
nulls).  Instead we'll store the data as a []byte array and consumers
can convert to a string - via string(value) - as required.

Addresses issue #23
fix errorf in marshal.go

author: @virtuallynathan
'go test' not non-verax-tests.sh

* rm non-verax-tests.sh, Travis
* separate verax directory
* disable TestGenericWalk
* update readme's
Merge branch soniah 'master' into codedance_master