docs(readme): add a license badge to README.md
docs(readme): add a license badge to README.md

1. Add a shields.io license badge to allow quick, effective identification
   of the license without requiring the user to scroll to the bottom of the
   page.
2. Remove the single-word license section at the bottom of the page as it
   is now superfluous and looks unpolished.
3. Move the crates.io badge beyond the license badge so that its orange
   colour won't knock the viewer's brain off fast-path evaluation when
   using the badge row as a status dashboard (as explained in #525).

Fixes #525

mfeckie/hyper,Twey/hyper,achanda/hyper,tempbottle/hyper,bonifaido/hyper,tshepang/hyper,clatour/hyper,sfackler/hyper,yangxingpping/hyper,hyperium/hyper,Keats/hyper,fengsp/hyper,lame-nickname/hyper,giftcards/hyper,hyperium/hyper,tshepang/hyper,Keats/hyper,Twey/hyper,steveklabnik/hyper,nickgonzales/hyper,nickgonzales/hyper,golddranks/hyper,markuskobler/hyper,mneumann/hyper,yazaddaruvala/hyper,hannobraun/hyper,jmmaranan/hyper,golddranks/hyper,nickgonzales/hyper,ianks/hyper,Twey/hyper,markuskobler/hyper,softprops/hyper,TimNN/hyper,rschulman/hyper,mre/hyper,pyfisch/hyper,manuel-woelker/hyper,hannobraun/hyper,reem/hyper,bheesham/hyper,golddranks/hyper,fuchsnj/hyper,hyperium/hyper,fhahn/hyper,erickt/hyper,Keats/hyper,markuskobler/hyper,tshepang/hyper,youprofit/hyper,mitsuhiko/hyper,hannobraun/hyper,yazaddaruvala/hyper,peterhj/hyper