The present invention relates to compounds of formula I: and pharmaceutically acceptable salts thereof, wherein R1, R2 and R3, are as defined herein. The invention also relates to pharmaceutical compositions comprising these compounds, methods of using these compounds in the treatment of various diseases and disorders, processes for preparing these compounds and intermediates useful in these processes.本發明係關於式I化合物：及其醫藥上可接受之鹽，其中R1、R2及R3係如本文定義。本發明亦關於包括此等化合物之醫藥組合物、使用此等化合物於治療各種疾病及病症的方法、用於製備此等化合物的方法及適用於此等方法之中間體。
