DOC: Use consistent lowercase on docs landing page
DOC: Use consistent lowercase on docs landing page

Corrects titles to all use sentence case, per style guide.

grlee77/numpy,mhvk/numpy,madphysicist/numpy,madphysicist/numpy,endolith/numpy,pbrod/numpy,pbrod/numpy,grlee77/numpy,pdebuyl/numpy,endolith/numpy,simongibbons/numpy,pdebuyl/numpy,jakirkham/numpy,seberg/numpy,jakirkham/numpy,pdebuyl/numpy,mhvk/numpy,anntzer/numpy,numpy/numpy,pbrod/numpy,rgommers/numpy,charris/numpy,charris/numpy,numpy/numpy,mhvk/numpy,simongibbons/numpy,anntzer/numpy,charris/numpy,madphysicist/numpy,pbrod/numpy,anntzer/numpy,grlee77/numpy,numpy/numpy,jakirkham/numpy,grlee77/numpy,simongibbons/numpy,mattip/numpy,endolith/numpy,numpy/numpy,simongibbons/numpy,rgommers/numpy,mattip/numpy,mhvk/numpy,seberg/numpy,pbrod/numpy,rgommers/numpy,jakirkham/numpy,seberg/numpy,mattip/numpy,anntzer/numpy,rgommers/numpy,seberg/numpy,mhvk/numpy,simongibbons/numpy,grlee77/numpy,charris/numpy,madphysicist/numpy,jakirkham/numpy,endolith/numpy,mattip/numpy,madphysicist/numpy,pdebuyl/numpy