fix location of vignettes as per CRAN requests

This is a first attempt to fix the location of vignettes as per the CRAN requests. Couple of points: 

- I'm not sure if the binary PDF files should actually be removed

- Building the tar archive seems to work fine: 

    ==> R CMD build latticist

    * checking for file ‘latticist/DESCRIPTION’ ... OK
    * preparing ‘latticist’:
    * checking DESCRIPTION meta-information ... OK
    * installing the package to build vignettes
    * creating vignettes ... OK
    * checking for LF line-endings in source and make files
    * checking for empty or unneeded directories
    * building ‘latticist_0.9-44.tar.gz’



- And the changes get rid of all vignette-related Notes/Warnings from the CRAN checks. There are two code-related Notes left, but I haven't investigated those. 

    ==> R CMD check latticist_0.9-44.tar.gz

    * using log directory ‘/home/geek/Build/Devel/latticist.Rcheck’
    * using R version 3.0.2 (2013-09-25)
    * using platform: x86_64-pc-linux-gnu (64-bit)
    * using session charset: UTF-8
    * checking for file ‘latticist/DESCRIPTION’ ... OK
    * checking extension type ... Package
    * this is package ‘latticist’ version ‘0.9-44’
    * checking package namespace information ... OK
    * checking package dependencies ... OK
    * checking if this is a source package ... OK
    * checking if there is a namespace ... OK
    * checking for executable files ... OK
    * checking for hidden files and directories ... OK
    * checking for portable file names ... OK
    * checking for sufficient/correct file permissions ... OK
    * checking whether package ‘latticist’ can be installed ... OK
    * checking installed package size ... OK
    * checking package directory ... OK
    * checking DESCRIPTION meta-information ... OK
    * checking top-level files ... OK
    * checking for left-over files ... OK
    * checking index information ... OK
    * checking package subdirectories ... OK
    * checking R files for non-ASCII characters ... OK
    * checking R files for syntax errors ... OK
    * checking whether the package can be loaded ... OK
    * checking whether the package can be loaded with stated dependencies ... OK
    * checking whether the package can be unloaded cleanly ... OK
    * checking whether the namespace can be loaded with stated dependencies ... OK
    * checking whether the namespace can be unloaded cleanly ... OK
    * checking loading without being on the library search path ... OK
    * checking dependencies in R code ... NOTE
    Packages in Depends field not imported from:
      ‘lattice’ ‘latticeExtra’ ‘vcd’
      These packages needs to imported from for the case when
      this namespace is loaded but not attached.
    See the information on DESCRIPTION files in the chapter ‘Creating R
    packages’ of the ‘Writing R Extensions’ manual.
    * checking S3 generic/method consistency ... OK
    * checking replacement functions ... OK
    * checking foreign function calls ... OK
    * checking R code for possible problems ... NOTE
    latticeStyleToBasePar : setAlpha: warning in rgb(crgb[1], crgb[2],
      crgb[3], crgb[4], max = 255): partial argument match of 'max' to
      'maxColorValue'
    latticistCompose : doCompose : deparse1: warning in deparse(expr, width
      = 500, control = NULL, backtick = TRUE): partial argument match of
      'width' to 'width.cutoff'
    latticeStyleGUI: no visible binding for global variable ‘category’
    * checking Rd files ... OK
    * checking Rd metadata ... OK
    * checking Rd cross-references ... OK
    * checking for missing documentation entries ... OK
    * checking for code/documentation mismatches ... OK
    * checking Rd \usage sections ... OK
    * checking Rd contents ... OK
    * checking for unstated dependencies in examples ... OK
    * checking sizes of PDF files under ‘inst/doc’ ... OK
    * checking installed files from ‘inst/doc’ ... OK
    * checking files in ‘vignettes’ ... OK
    * checking examples ... OK
    * checking for unstated dependencies in vignettes ... OK
    * checking package vignettes in ‘inst/doc’ ... OK
    * checking running R code from vignettes ...
       ‘latticistAids2.Rnw’ ... OK
       ‘latticistCO2.Rnw’ ... OK
       ‘latticistEmployment.Rnw’ ... OK
       ‘latticistFrogs.Rnw’ ... OK
     OK
    * checking re-building of vignette outputs ... OK
    * checking PDF version of manual ... OK
    NOTE: There were 2 notes.