Taxonomy API

New Feature:
Integerated with Taxonomy API.
supporting getDefaultCategoryTreeId, getCategoryTree, getCategorySubtree, getCategorySuggestions.

Bug fixes

Bug Fix. Fixed Issue #4

Browse Api

Using the Browse API, you can create a rich selection of items for your buyers to browse with keyword and category searches.
The Browse API lets shoppers search for specific items by keyword, category, product, or item aspects and retrieve the details of an item.

1. getItem.
2. getItembylegacyid.
3. getItembygroupid.

Access token and browse api's.

Simplified getting Access token.
exposing Browse api's using access token.
modified readme.

Testing using nock

added test.
updated ReadMe file.

initial release

V1.0.0

merging travis yml