code format cosmetic
update Rd; rab passed
double quote to single quote
demo/example cosmetic
closes #37: using highlight.js
closes #33: factor out function 'comp_pdf' from 'saveGIF', 'saveLatex' and 'saveSWF'
closes #34: factor out 'auto_browse' from 'saveSWF', 'saveVideo' and 'im.convert.R'
closes #36: factor out the code to find ImageMagic/GraphicsMagic
closes #35: 'shQuote' is invoked internally in 'im.convert'
file.rename -> file.copy
minor revisions
Merge pull request #41 from mingsnu/master

code cosmetic & issue 33 - 37