Weave related issues

[isaacsas]

1. using Plots.jl with PyPlot and fmt=:svg the generated html file uses png files. The notebook seems to use svg.
2. Latex generation is somehow not creating a figure folder that is then referenced in the .tex file. Specifically, the figure

 \includegraphics[width=\linewidth {/Users/isaacsas/.julia/dev/DiffEqTutorials/pdf/models/tmpICR6PZ/diffeqbio_I_introduction_10_1.pdf}

is missing when compiling latex. Note, my latex compile fails initially due to Latexify using the mhchem package and including a necessary command in the generated environment that is mathjax specific. I was initially able to edit the .tex file and get it to compile as the missing figure issue wasn't happening. After deleting all the Latex output, including tmp file folders, to try to start over I am getting this issue (even in a new REPL). I also upgraded to the latest master.

[isaacsas]

1. can be fixed by explicitly telling Weave to use svg output, i.e. passing weave fig_ext=".svg".
2. can be fixed by setting mathjax=false in Latexify, which allows the tex to compile with properly generated figures.