Add unit and grid.draw to grid imports

This satisfies a note from `R CMD CHECK` about global functions with no visible
bindings.
Set default CRAN mirror for make deps task

We need a mirror set or R will simply roll over and die with an error.
Add package arguments to metrics functions

`getLatexStrWdith` and `getLatexCharMetrics` now take `documentDeclaration` and
`packages` as parameters.
Pass package arguments from C functions

Pass `documentDeclaration` and `packages` when `getLatexStrWidth` and
`getLatexCharMetrics` are called from the C level. This ensures these arguments
are honored if passed to `tikz` when the device is created.

Fixes #59.
Merge docs for getLatexStrWidth and getLatexCharMetrics

Both functions do pretty much the same thing---no sense in maintaining two
manpages that are 90% identical.
Fix multiple function documentation in tikzAnnotate.R

Proper roxygen2 way to mark multiple functions for consolidation in the same
`.Rd` file is to use the `@rdname` directive.
Fix quotes in makefile `deps` task
make check: Run R CMD check with --as-cran

Adding the `--as-cran` flag enables additional checks that get run on the CRAN
servers.
make vignette: Compact PDF files after creation

Requires qpdf and ghostscript to be installed. This cuts the size of the
vignette PDF by ~50% and prevents some CRAN warnings.
Pass lib.loc to getTikzDeviceVersion

When packages are loaded from a directory not on the R library path, such as by
using `library(..., lib.loc = '/some/directory')`, then functions like
`system.file` don't work correctly unless `lib.loc` is passed.

This fixes a CRAN warning in R-devel.
make release: Don't edit temporary merge message

This message gets overwritten later with a proper commit message.
getDocumentPointsize: fix regexp

The previous regexp would match any number that was followed by either
"p" or "t" and use this as the document point size.  This led to

    \documentclass[a4paper]{artice}

being interpreted as a 4pt document.  As a result, plotted figures
wound up with grossly scaled font nodes (scale=3 or similar).

We instead want to only match digits at the beginning of a word,
followed by the string "pt".
only match digits+"pt" for point size
start an RStudio project
roxygenize
head() has been exported from utils, so :: instead of :::
let's use semantic versioning in DESCRIPTION, and get rid of this home-made strategy

http://yihui.name/en/2013/06/r-package-versioning/
starup message should appear in .onAttach() instead of .onLoad()

in the future we may do it, but for now, I just remove the startup messages
mv inst/doc to vignettes/
bump version, and clarify authorship/maintainership