Allow inverted charset

[joelnb]

Allow easily using an inverted charset 0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ - some other implementations online (e.g. this Java one) use the charset in a different order. This code provides a new constant for this type of charset & allows the user to specify which charset to use on all calls (while leaving the current defaults unchanged).

I originally wrote this based on the develop branch but that has quite a few commits which are not in master so I changed it to be against master. Happy to rebase if you would prefer this PR go to develop instead.

[coveralls]

Coverage increased (+1.9%) to 91.228% when pulling 82a0e2d on joelnb:allow-inverted-charset into 1d1a9d7 on suminb:master.

[coveralls]

Coverage increased (+0.03%) to 98.246% when pulling 44331f7 on joelnb:allow-inverted-charset into 1bb3a24 on suminb:develop.

[suminb]

Looks good to me. Thanks for your work! I'd like to make a couple of requests though:

• Submit this PR to develop branch
• Fix ValueError: embedded null byte exceptions in Python 3.6

[joelnb]

Hi @suminb thanks for your original work on this also - saved me a lot of time!

I've changed the PR to be against develop but would you mind explaining what you mean by the second part? I've not come across that exception so far using this library & I've run the tests both before & after the rebase to develop.

[suminb]

would you mind explaining what you mean by the second part?

Your build was failing when you first submitted this PR, but it appears that the issue has been resolved somehow 🤔

Now GitHub is telling me there are conflicts in base62.py. If you could resolve this, we're good to go.

[joelnb]

I've resolved the conflict now but thought it's worth mentioning what the conflict was - I had changed the __version__ from 0.3.2 to 0.4.0 (to denote the relatively large change) but you have now released 0.3.3. I resolved the conflict to keep the 0.4.0 version I originally added but happy to back that out & leave as 0.3.3 if you prefer.

[joelnb]

Also I had a look at the travis issue you mentioned - I can't reproduce that & it has not happened this time so not sure about the reasons for that one.

[suminb]

I've resolved the conflict now but thought it's worth mentioning what the conflict was - I had changed the version from 0.3.2 to 0.4.0 (to denote the relatively large change) but you have now released 0.3.3.

Correct. I should've informed you about that. My apology for the inconvenience.

I resolved the conflict to keep the 0.4.0 version I originally added but happy to back that out & leave as 0.3.3 if you prefer.

We (in this project, we mostly refers myself) generally change the version info in a release branch. No need to revert your code back though. I'll try to write up some guideline with regard to submitting PRs and enforce the rules thereafter.