Add intro for article “Introduction to XMLHttpRequest Level 2”
Add intro for article “Introduction to XMLHttpRequest Level 2”

Ref. #19.

paulirish/devopera,payeldillip/devopera,michaelstewart/devopera,payeldillip/devopera,simevidas/devopera,SelenIT/devopera,kenarai/devopera,operasoftware/devopera,payeldillip/devopera,operasoftware/devopera,initaldk/devopera,SelenIT/devopera,simevidas/devopera,Jasenpan1987/devopera,simevidas/devopera,Mtmotahar/devopera,payeldillip/devopera,operasoftware/devopera,paulirish/devopera,cvan/devopera,Jasenpan1987/devopera,cvan/devopera,michaelstewart/devopera,Jasenpan1987/devopera,SelenIT/devopera,paulirish/devopera,simevidas/devopera,operasoftware/devopera,erikmaarten/devopera,andreasbovens/devopera,shwetank/devopera,erikmaarten/devopera,Mtmotahar/devopera,kenarai/devopera,michaelstewart/devopera,cvan/devopera,andreasbovens/devopera,paulirish/devopera,shwetank/devopera,Mtmotahar/devopera,kenarai/devopera,SelenIT/devopera,andreasbovens/devopera,initaldk/devopera,cvan/devopera,Jasenpan1987/devopera,kenarai/devopera,erikmaarten/devopera,Mtmotahar/devopera,erikmaarten/devopera,shwetank/devopera,initaldk/devopera,initaldk/devopera,michaelstewart/devopera