added experiment-dir param to flexp-browser

[tivvit]

fixes #14

did a little cleanup in the file too

[tomasprinda]

There is some problem with TxtToHtml module. Check screenshot.

All experiments are red - it is done by checking if some file exists in the folder. If not, it is red so the file is not found even if it is there.

I ran it by

flexp-browser --experiments_dir experiments/

To get the exception message you can use

git rebase 20-show-exception-message-in-to_html_2

[tivvit]

i will take a look at it

[tomasprinda]

Then we can also edit the documentation.

[tomasprinda]

MR #31 is update of this MR.