Make pandas optional

[gutzbenj]

Dear @gadomski ,

this PR makes pandas optional (still installable via isd[io])

[gutzbenj]

Dear @gadomski ,

please re-review :)

[gadomski]

@gutzbenj I can't push to your branch, but can you take up the changes in b117e40? Rather than use PR suggestions, I just made some edits. Mostly removing the pytest mark b/c I don't think it's necessary, and some spurious whitespace changes as well. Thanks!

[gutzbenj]

Dear @gadomski ,

I really can't seem to understand your policy here. You said before that

• (regardless of the PR) you want to have as little diff as possible
• if pandas is optional the lib should be tested with and without it being installed

though the commit you did both

• introduces unnecessary diff by removing the blank lines
• removes the steps in CI that test without and with pandas being installed

Also, the marker should just be helpful - which it is per se.

I'm really confused now, please clear my worries 😵‍💫

[gadomski]

I'm really confused now, please clear my worries 😵‍💫

Yeah, I apologize @gutzbenj, thanks for your patience. I only come back to this project every once in a while and sometimes I forget previous decisions I've made 🙃 . To avoid further confusion, I've rolled up both of these PRs with my current way of thinking into #47. Thanks for your contribution!