Stuff all vignette preamble junk into a new style file

This makes it easier to get to the meat of the paper without scrolling through
all the preamble business. Also makes it possible to adjust preamble parameters
and re-typeset without having to re-run Sweave.

The old `tikzDeviceMacros` file has been combined into the new style file.
Use the Memoir class for the vignette

Use Memoir instead of the standard LaTeX `article` class. Currently using
Memoir in article mode, but may transition to a different mode more suitable
for printing.
Re-do section levels

Section levels in Memoir start with chapter instead of section.
Setup vignette header and footer

Nice ruled header with chapter name and page number. Footer with package name
and description.
Style chapter and section headers

The look of the chapter and section headers is modeled after the tkz-doc class
by Alain Matthes.
Revise Loading the Package chapter

 - Updated package loading method.

 - Changed explanation of how and why the tikzDevice searches for compilers.

 - Added notes and options related to LuaTeX.
Revise vignette cover page

The vignette cover page was laid out using a lot of weird calculations and
positioning hacks that probably make no sense to anyone but me.

This revision cleans up the code and moves a few pieces of info such as the
authors, date and package version onto the cover page.

Commands such as `\author` and `\title` that get inserted into the PDF metadata
have been cleaned up.
Update tikzCodeBlock to v0.2
Revise Introduction chapter

  - Pulled beta notice as it is extremely unlikely that the public API will change before
    version 1.0 and the package has been in existance for 2+ years so the word
    "beta" is a bit silly at this point.

  - Added an example comparing the default output of `pdf` and the default
    output of `tikz`. This example is very biased and should be re-worked to
    show how hard it is to get `pdf` to use TeX fonts and how easy it is to get
    `tikz` to do the same job.

  - Some re-wording edits and other misc. cleanups.
Add list of required LaTeX packages

Useful for people who don't have a full TeX install.
Added it at the start of the "Installing TikZ" section.

Also, corrected two-or-so typos.
Revise Loading the Package chapter

 - Updated package loading method.

 - Changed explanation of how and why the tikzDevice searches for compilers.

 - Added notes and options related to LuaTeX.
Update tikzCodeBlock to v0.2
Merge pull request #58 from sietse/maintenance/refactor-vignette

Add list of required packages for users who do not use a full TeX installation.
Remove ulem package from vignette

This was only used in one place for a strikethrough effect. Unfortunately,
loading the package also messes with a bunch of macros, such as `\emph`.
Revise tikz chapter

Revised chapter concerning the tikz function. In addition to general edits:

  - Updated the description of tikz options.

  - Made sure all code examples use `TRUE` and `FALSE` instead of `T` and `F`.
Revise XeLaTeX example in vignette

Example was ancient---still triggered the xelatex compiler by overloading
package options. Converted to an Sweave code chunk with `eval` set to FALSE and
fixed numerous bugs.
Style part divisions
Revise bareBones example

Now using the `tikzCoord` function which is much less verbose than using
`tikzAnnotate` directly.
Revise metric function chapter
Upgrade tikzCodeBlock to 0.3