Add documentation

[tshort]

The documentation was pulled straight out of Vincent's repository with no reorganization. This organization can be used directly by the following help package:

https://github.com/tshort/HelpTestbed.jl

The documentation can be browsed on github, but it's not the best organization for that. The .rst files are rather buried.

There is a _JLINDEX files that maps help keywords to file location and a one-line description. This is searched by apropos and used by @help.

Here is a quick example using the help package above:

julia> apropos("RDatasets", "iris")
RDatasets       iris        Edgar Anderson's Iris Data
RDatasets       Bowley      Bowley's data on values of British and Irish trade, 1855-1899

julia> @help iris
iris not defined

julia> @help RDatasets iris
m.captures  = ["iris", "datasets/iris", "Edgar Anderson's Iris Data"]
Package `RDatasets`,  iris

Edgar Anderson's Iris Data

+--------+-------------------+
| iris   | R Documentation   |
+--------+-------------------+

Edgar Anderson's Iris Data
 --------------------------

Description

This famous (Fisher's or Anderson's) iris data set gives the
measurements in centimeters of the variables sepal length and width and
petal length and width, respectively, for 50 flowers from each of 3
species of iris. The species are *Iris setosa*, *versicolor*, and
*virginica*.

{stuff snipped...}

[johnmyleswhite]

Pulling now. We can debate alternatives at a later time.