Multiple Fixes & GoDoc Descriptions

[rmenn]

Fixed a couple of bugs that i myself created.
Added Description for godoc
Added VpcId to Create Security Group so that SGs can be created within VPC.

Please Review.

Thanks

[rmenn]

If all Good, Can close #135

[alimoeeny]

Thanks @rmenn
Does it make sense to keep the signature for CreateSecurityGroup intact and add another function like CreateSecurityGroupInVPC
Although we don't have a guideline for this, I feel uncomfortable about this. and "traditionally" people have added functionality by keeping the old functions and adding new ones.
Soon we need to sit down and plan a next major release and cleanup all of these.

[rmenn]

Makes Sense, Let me redo that.