Switch to Cobra

Also:
- Fixed the Makefile
- Added a Taskfile.yml (see: https://taskfile.dev)
- Updated the manual page

Signed-off-by: Shin'ya Minazuki <shinyoukai@laidback.moe>

Makefile

@@ -1,13 +1,10 @@
-VERSION = `git describe --tags` || echo MIRAI
-
 GO = go
-GOFLAGS = -v -buildvcs=false -buildmode=exe -ldflags "-w -X `${GO} list`.Version=${VERSION}"
+GOFLAGS = -v -buildvcs=false -buildmode=exe -ldflags='-w -X "`${GO} list`.Version=${VERSION}" -X "`${GO} list`.Revision=${REVISION}"'
 
-build: mikuru-login mikuru-post
+VERSION ?= `git describe --tags`
+REVISION ?= `git rev-list --all | wc -l`
 
-mikuru-login:
-	${GO} build ${GOFLAGS} ./cmd/$@
-mikuru-post:
-	${GO} build ${GOFLAGS} ./cmd/$@
+build:
+	@${GO} build ${GOFLAGS} -o mikuru ./cmd
 clean:
-	rm -f mikuru-*
+	@rm -f mikuru