Option to ignore whitespace

[GiovanH]

Whitespace is left in place. Only lines with content are deduplicated.

The ignore list could potentially be extended to be configurable.

[ilyakam]

Hello @GiovanH and thank you for the contribution! Apologies for not getting back to you about this sooner.

There are a few things that I'd like to address with regards to this PR and to hear your thoughts about them.

1. What problem are you trying to solve?
   As seen in the Order of Operations section of the CONTRIBUTING.md document, I'd prefer it if you started by describing the issue. Based on the code and the description above, it sounds like you don't wish to consider empty lines as duplicates of one another. If so, may I ask why? Multiple lines with no characters are technically duplicates of one another, are they not? Moreover, I'm in the process of moving over to VS Code and another plugin called Text Power Tools that was developed independently from this one (to the best of my knowledge) is acting in the exact same way:

ST3	VSC

2. You mentioned that "[t]he ignore list could potentially be extended to be configurable." I agree! If you can convince me of the use case in the previous question, then there's already a pattern that allows you to customize the settings. Please take a look at the *.sublime-settings files in my other ST3 plugins, NumberFormatter and ParentalControl. The gist is this code. In my opinion, that's much better than having a hardcoded regex that can only be changed by releasing an update to this plugin.

3. Thanks for including a separate "Basic hygiene" commit (49e4a0d)! Having reviewed this section of the PEP8 guide, it looks like I need to update the following .editorconfig rule:

   RemoveDuplicateLines/.editorconfig

   Line 8 in deb1f3c

   indent_size = 2

   I'm going to open a new issue for that. EDIT: Adhere to the PEP8 Style Guide #29

[GiovanH]

My apologies, this was supposed to still be a draft PR. Yes, I agree with making the ignorelist a configurable setting, and it should probably be empty by default. This was one of those "I wrote it, so let me make a note before I forget" situations.