chore: Prepare for v0.6.0 (google#64)

chore: Prepare for v0.5.1. (google#46)

chore: Prepare for v0.5.0 (google#43)

Prepare for v0.4.0. (google#26)

Prepare for v0.3.1. (google#23)

Prepare for v0.3.0. (google#20)

Only recognize well-known comment markers (google#11)

Restricting what comment markers keep-sorted accepts leads to less
surprising behavior, such as // go/keep-sorted treating the comment
marker as "// go/" when using the default id of just "keep-sorted".

Move golden_test into a proper test directory. (google#5)

Fix a typo in the README. (google#3)