version: Move version information into a separate package.

This will allow it to be accessed by other sections of the code.

Dockerfile

@@ -3,7 +3,7 @@ FROM alpine:edge AS builder
 COPY . /go/src/matterbridge
 RUN apk --no-cache add go git \
         && cd /go/src/matterbridge \
-        && CGO_ENABLED=0 go build -mod vendor -ldflags "-X main.githash=$(git log --pretty=format:'%h' -n 1)" -o /bin/matterbridge
+        && CGO_ENABLED=0 go build -mod vendor -ldflags "-X github.com/42wim/matterbridge/version.GitHash=$(git log --pretty=format:'%h' -n 1)" -o /bin/matterbridge
 
 FROM alpine
 RUN apk --no-cache add ca-certificates mailcap