Fix issue with vignettes

In version 2.1.0 the directory which contains compiled versions of the vignettes was not updated. This patch version fixes that issue as well as a small typo in the wdi_choropleth documentation.

v2.1.0

-Add admin1_choropleth function which allows you to create an Administrative Level 1 choropleth of any
country in the world. (Administrative Level 1 is the generic term for states, provinces, etc.). Create
a vignette demonstrating usage of this function.
-Add function county_zoom_choropleth, which allows you to zoom in on counties, not states. If an individual county is specified, render it with no fill color.
-Updated and corrected the values of df_president. Thank you to Richard Careaga.
-Update vignettes about US maps. Specifically, provide information about custom scales to include warning about interactions with insets of AK and HI.

Rewrite using R6, Support for WDI, arbitrary shapefiles

This version breaks backwards compatability. I recommend reading the vignettes to see documentation on how to use the features which you normally use in the package, as well as an explanation of the new features. Also see the NEWS file for a list of changes..

World Map

FEATURE
-Add a world map: see ?map.world for more info
-Add a vector of all countries in the world map: see ?country.names for more info
-Add support for the world map to the choroplethr() function: see ?choroplethr for more info.

Render Alaska and Hawaii as insets for state and county maps

FEATURE
-Add a flag to the choroplethr() function, renderAsInsets. If TRUE and user asked to view all
states, then AK and HI will be rendered as insets, which is the standard way of rendering a map of
all 50 US states.
-Create a data.frame, map.states, which contains a map for all 50 states plus the District of Columbia. See ?map.states for details.
-Create a data.frame, state.names, which contains naming information for each state in map.states. See ?state.names for more information.
-Create a data.frame, map.counties, which contains a map for the counties of all 50 states plus the District of Columbia. See ?map.counties for details.
-Create a data.frame, county.names, which contains naming information for each county in map.counties. See ?county.names for more information.

Handful of small improvements

Version 1.5.0 has a handful of minor changes:
-NA values now appear black. The previous value of grey50 (the default NA color in ggplot2) was difficult to distinguish from light values in the brewer scale, which is the default scale in choroplethr.
-Create function clip_df(data.frame, lod) that clips a data.frame to a map. This is useful
when you want to do statistics on a data.frame (such as above/below median values), and have your computations match the map. For example, maps in choroplethr do not contain Alaska or Hawaii.
-Rename vignettes so that they appear in proper order on CRAN website.
-Export format_levels function.

BUG FIXES
-handle counties with leading zeroes.

animated choropleths, vignettes, built in data

More details about this release can be found here: https://groups.google.com/forum/#!topic/choroplethr/gTKhxrr_rVA

1. Support for animated choropleths. Type ?choroplethr_animate to see a runnable example of animating a choropleth of all US election results ever.
2. choroplethr now ships with example datasets. Type data(choroplethr) to access them, and type ?<data set> to get more information about an individual dataset.
3. Example files now use built-in datasets, and so can run as-is.
4. choroplethr now ships with 6 vignettes. You can access them by
   • typing browseVignettes(package="choroplethr") from the command-line
   • Viewing them on the wiki: https://github.com/trulia/choroplethr/wiki
   • Viewing them on the CRAN page for choroplethr: http://cran.r-project.org/web/packages/choroplethr/index.html

Manual values

Give users more support for setting bucketing / coloring strategies for choropleths, which was the most requested feature. See this blog post for details: http://www.trulia.com/tech/2014/03/10/introducing-choroplethr-version-1-2-0-2/

subset states, "any" acs, first CRAN release

1. First version available on CRAN
2. Ability to view subsets of states at the state, county and zip lod
3. Ability to view any acs available via the census api, not just the 2011 5 year survey.

See this blog post for details: http://tech.truliablog.com/2014/02/14/choroplethr-version-1-1-0-released/

Add requirement of R version 3.0.0 minimum

Add explicit R minimum version of 3.0.0. This will hopefully prevent the most common bug report that I have been receiving: https://groups.google.com/forum/#!topic/choroplethr/Owv7NgAacGE