Plotting of text in logarithmic scale (Closes #986)

[ronaldremmerswaal]

As described in issue #986, plotting text in logarithmic scale can yield undesired effects. E.g.
text(0.5, 1E-8, 'hi') results in 'hi' placed at (0.5, 0) since

matlab2tikz/src/matlab2tikz.m

Line 6700 in 62a038d

value = round(value/tolerance)*tolerance;

results in value = 0.
If value was 1E-6, then this line would not change value, but

matlab2tikz/src/matlab2tikz.m

Line 6708 in 62a038d

str = sprintf('%.3f', value);

would still print the string '0'.