Change phrasing and formatting of README
Change phrasing and formatting of README

Made a few changes to the README to emphasize Pelican's position as a
general-purpose static site generator, and not just a blogging tool.

See #1645 for more details.

Rogdham/pelican,iurisilvio/pelican,TC01/pelican,treyhunner/pelican,catdog2/pelican,treyhunner/pelican,eevee/pelican,getpelican/pelican,zackw/pelican,Scheirle/pelican,janaurka/git-debug-presentiation,UdeskDeveloper/pelican,rbarraud/pelican,JeremyMorgan/pelican,simonjj/pelican,jvehent/pelican,lazycoder-ru/pelican,lucasplus/pelican,florianjacob/pelican,joetboole/pelican,iurisilvio/pelican,number5/pelican,kennethlyn/pelican,koobs/pelican,JeremyMorgan/pelican,gymglish/pelican,lucasplus/pelican,garbas/pelican,iurisilvio/pelican,simonjj/pelican,btnpushnmunky/pelican,avaris/pelican,HyperGroups/pelican,catdog2/pelican,gymglish/pelican,Polyconseil/pelican,abrahamvarricatt/pelican,ls2uper/pelican,jvehent/pelican,janaurka/git-debug-presentiation,talha131/pelican,btnpushnmunky/pelican,eevee/pelican,UdeskDeveloper/pelican,talha131/pelican,levanhien8/pelican,abrahamvarricatt/pelican,11craft/pelican,goerz/pelican,ls2uper/pelican,goerz/pelican,kennethlyn/pelican,eevee/pelican,number5/pelican,GiovanniMoretti/pelican,deved69/pelican-1,HyperGroups/pelican,lazycoder-ru/pelican,goerz/pelican,deanishe/pelican,getpelican/pelican,number5/pelican,deanishe/pelican,GiovanniMoretti/pelican,koobs/pelican,JeremyMorgan/pelican,Scheirle/pelican,iKevinY/pelican,Summonee/pelican,rbarraud/pelican,alexras/pelican,catdog2/pelican,ingwinlu/pelican,51itclub/pelican,ehashman/pelican,florianjacob/pelican,joetboole/pelican,alexras/pelican,deved69/pelican-1,kennethlyn/pelican,farseerfc/pelican,jimperio/pelican,51itclub/pelican,Polyconseil/pelican,11craft/pelican,alexras/pelican,ingwinlu/pelican,iKevinY/pelican,zackw/pelican,lucasplus/pelican,deved69/pelican-1,51itclub/pelican,gymglish/pelican,florianjacob/pelican,janaurka/git-debug-presentiation,crmackay/pelican,karlcow/pelican,karlcow/pelican,UdeskDeveloper/pelican,abrahamvarricatt/pelican,crmackay/pelican,joetboole/pelican,Scheirle/pelican,GiovanniMoretti/pelican,jimperio/pelican,koobs/pelican,levanhien8/pelican,farseerfc/pelican,jvehent/pelican,Rogdham/pelican,TC01/pelican,11craft/pelican,Summonee/pelican,crmackay/pelican,karlcow/pelican,douglaskastle/pelican,douglaskastle/pelican,deanishe/pelican,Rogdham/pelican,simonjj/pelican,garbas/pelican,garbas/pelican,Summonee/pelican,ls2uper/pelican,douglaskastle/pelican,zackw/pelican,lazycoder-ru/pelican,avaris/pelican,TC01/pelican,btnpushnmunky/pelican,rbarraud/pelican,ehashman/pelican,ehashman/pelican,treyhunner/pelican,HyperGroups/pelican,jimperio/pelican,levanhien8/pelican