Merge pull request #76 from kikocorreoso/master

Updated ES, EN and FR docs
Set default argument "encoding" of bytes.decode() to "utf-8" + fix bug in bytes.__add__
Set methods union(), difference() etc. accept any iterable as argument
In method format() of strings, set _is_numeric to True for floats and integers
Fix bug with implicit concatenation of literal bytes
Latest version of brython.js
Update documentation of the javascript module
update javascript.md to the latest version