Prepare changelog for v0.6.3
Prepare changelog for v0.6.3

matrix-org/matrix-js-sdk,williamboman/matrix-js-sdk,williamboman/matrix-js-sdk,matrix-org/matrix-js-sdk,krombel/matrix-js-sdk,matrix-org/matrix-js-sdk,krombel/matrix-js-sdk,williamboman/matrix-js-sdk,krombel/matrix-js-sdk,matrix-org/matrix-js-sdk