make README more consise

[charlierudolph]

@aearly

• remove unneeded documentation about series/limit
  • every command reexplains what it does
• shorten the list of commands by grouping those very similar
  • makes it easier to scan the list and see all the functionality the library provides

[aearly]

👍 for this, especially because I want to add limit and series variations for more methods.

I also now realize that there's nowhere where it actually explains what the difference is between the fooLimit and fooSeries variants. I think we need a section explaining that many methods are parallel by default, and then with limit and series versions.

[charlierudolph]

I added the little blurb about Limit and Series above the list of functions. Is that enough or what else are you looking for?

[aearly]

Cool, that works.