Enable Travis CI integration.

See https://travis-ci.org/

The changes here enable Travis CI integration for https://github.com/jimlloyd/gremlin-node.
Anthony will need to setup his Travis account and then edit the line in README.md to
reference his own repo.

I.e. replace jimlloyd with inolen in this bit of markdown:
[![Build Status](https://travis-ci.org/jimlloyd/gremlin-node.svg)](https://travis-ci.org/jimlloyd/gremlin-node)
Upgrade to TinkerPop v2.5.
Merge pull request #69 from jimlloyd/feature/upgrade-to-tinkerpop-2.5

Feature/upgrade to tinkerpop 2.5
updating travis-ci url
trigger travis-ci build
Bump up timeout on pipeline-wrapper filter to 5000ms.

The test sometimes takes longer than 2500ms on Travis.
Increasing to 5000s even though 3000ms might be enough,
as I don't want to have to keep bumping it up in the future.
Merge pull request #70 from inolen/feature/longer-travis-timeout

Bump up timeout on pipeline-wrapper filter to 5000ms.
Fix link to Travis in README.md.

The link refers to the repo in two places, but had been updated in
only one location. Now both locations refer to this repo.
Merge pull request #71 from inolen/feature/fixis-travis-link-in-readme

Fix link to Travis in README.md.
Fix some problems found while exercising the gremlin-console.

1. A better test for whether toJSONSync() can be called on the result.
(FYI there were cases that caused the other method to crash).

2. Add 'T' (gremlin.Tokens) to context to support T.eq, T.lt, etc.

3. Fix ElementWrapper.toJSON().
The prior implementation appeared to be a stub. It didn't use a callback
function which caused problems. The new unit test 'v(id) with single id then toJSON'
failed with the prior implementation, but succeeds with the new implementation,
which is modeled directly after PipelineWrapper.toJSON.
Merge pull request #72 from jimlloyd/feature/fix-console-4

Fix some problems found while exercising the gremlin-console.