make program pip installable

[rachmadaniHaryono]

here are some change to make the program installable

• the most notable is that readme which now using restructured text instead of markdown language
• the way the programm is called. after installed with pip, the program is called imgurdowload instead of python3 imgurdownload.py

[jtara1]

Looks good, but why the change to .rst?

[rachmadaniHaryono]

Pypi can only parse restructured text right now . To use markdown language on pypi, it need to be converted with pandoc and may cause undesired output

https://stackoverflow.com/questions/26737222/pypi-description-markdown-doesnt-work

E:actually I want to add parse subcommand that will print direct download url from album url, but after seeing the repo I decided to do clean up first. If it is finished I will create another pr

E2:~~just realize there is wrong formatted text in readme, will create another pr for this ~~

E3: just check it once again, and it is similar to previous markdown, so no pr for readme.