[Feature Request] Add high-level functionality for Entrez cgi DSLs

[kMutagene]

Low level functionality that requires knowledge of HttpFs and Hopac is implented since #84 .
Further abstraction would make it easier to use.

Additionally, most Entrez cgis provide the functionality of using a history server. When abstracting the current DSL, one should do it in such a way that the return results themself are pipe-able, meaning they can be used as further input for cgi queries. Here is an example from Entrez direct, where the result of esearch is the input for efetch:

esearch -db pubmed -query "lycopene cyclase" |
efetch -format abstract