Add information on filters, as well as checks

[beechnut]

Previously, there was no information in the README about filters, and running Serrano::Filters in a repl didn't provide any information (although we could read the code in the file).

This commit adds information about filters to the README, provides access to filter names and information in the library, and checks before running a request to make sure that filters are formatted as a hash and that the filters provided are valid filters.

[codecov-io]

Codecov Report

Merging #105 into master will increase coverage by 1.19%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #105      +/-   ##
==========================================
+ Coverage   87.69%   88.88%   +1.19%     
==========================================
  Files          20       21       +1     
  Lines         764      828      +64     
==========================================
+ Hits          670      736      +66     
+ Misses         94       92       -2

Impacted Files	Coverage Δ
lib/serrano/filters.rb	100% <100%> (+25%)	:arrow_up:
test/test_works.rb	100% <100%> (ø)	:arrow_up:
lib/serrano.rb	83.07% <100%> (+2.37%)	:arrow_up:
test/test_funders.rb	100% <0%> (ø)

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[sckott]

thanks @beechnut having a look

[beechnut]

@sckott, thanks for pointing out that filters can be used elsewhere, and I agree that it would be a good idea to add this check to those other routes. I'm a little slammed today but I should have that up in the next few days. :)

[sckott]

@beechnut ping