Update index.dok

Added <Use an empty string (2 apostophes in a row) if you want to keep the current value.> for keeping the current value of {xmin,xmax,ymin,ymax} in <gnuplot.axis> documentation. Actually, I don't know how to write the <''>, since these are a command in the documentation..
add documentation for gnuplot custom string
Merge branch 'master' of github.com:andresy/torch
add the new plot into repo
add wxt term for mac
Merge pull request #145 from Atcold/patch-1

Update index.dok
make default plot theme something nice
make sure to obey .gnuplot file if it exists
do not use filled style by default
Merge branch 'master' into luarocks