Update license to 3-clause BSD to match Discount 2.1.6. (#64)
Update license to 3-clause BSD to match Discount 2.1.6. (#64)

liangsun/discount,liangsun/discount,liangsun/rdiscount,liangsun/discount,liangsun/discount,liangsun/rdiscount,liangsun/rdiscount,liangsun/discount,liangsun/rdiscount