Checking in changes prior to tagging of version v0.99.0

v0.99.0 (2020-01-01)

• fix help docs #255 (Songmu)
• update documents #252 (Songmu)
• update deps #251 (Songmu)
• [incompatible] remove the "import" subcommand and merge this function into the "get" subcommand #244 (Songmu)
• [incompatible] drop look subcommand #243 (Songmu)
• [incompatible] make ~/ghq default root #237 (Songmu)
• add integration test for darcs #250 (Songmu)
• integration test on master #249 (Songmu)
• enhance svn and git-svn support #248 (Songmu)