Bump version to 0.3.0
Bump version to 0.3.0

bcremer/commonmark,fesor/commonmark,fesor/commonmark,garethellis36/commonmark,colinodell/commonmark,garethellis36/commonmark,postalservice14/commonmark,cebe/markdown-1,postalservice14/commonmark,stof/commonmark,hason/commonmark,kkiernan/commonmark,kkiernan/commonmark,hason/commonmark,thephpleague/commonmark,thephpleague/commonmark