Improve comments a little bit
Improve docs for setting up development environment
Allow using = in the end of an env var's value

Environment variables that contain an equal sign (=) in the end are
now matched. For example:

BASE64_STRING=t5urur0ck5==

This change breaks the usage of env-set. If a given value contains any
space, it *has* to be enclosed by either single or double quotes.

This is ensured by asserting the equality of both the number of arguments
provided by the shell (i.e. bash) and the number of matches found.

Test and usage example were updated accordingly.
Merge pull request #817 from scorphus/improvements

Allow using = in the end of an env var's value and some improvements