Better documentation about name, label and api-field

[huaiyumi]

These three fields can be different. Label is the term shown on the AnnoQ website. Name is the actual term used in the database. Api-field is the term used for api query.
Here is an example:

label: PEREGRINE_enhancer_linked_genes
name: enhancer_linked_genes
api_field: enhancer_linked_genes

Here the label is different from the name in the backend.

Here is another example:

name: 1000Gp3_AC
api_field: _1000Gp3_AC

Here the label and the name are the same, but api_field has an extra '_' added at the beginning, because api field can't start witha number.

The details of these mappings can be found at http://annoq.org/api-v2/annotations.

We need to provide more support to help users to handle these. Specifically,

1. We need to better documentation/instructions for developers who write api queries from command line or develop packages.
2. For end users who use packages, they just need to use the 'label' to query. Therefore, the packages should take care of it.

Please comment.