gnu: syncthing: Split into two outputs.

* gnu/packages/syncthing.scm (syncthing)[outputs]: New field.
[arguments]: Change the 'install' and 'install-docs' phases to install to the
two outputs.

gnu: syncthing: Use install-source? to disable installing the source code.

* gnu/packages/syncthing.scm (syncthing): Set #:install-source? #f
instead of deleting the install-source phase.

gnu: Add Syncthing.

* gnu/packages/syncthing.scm (syncthing): New variable.

gnu: Add go-golang-org-x-text-union.

* gnu/packages/syncthing.scm (go-golang-org-x-text-union): New variable.

gnu: Add go-golang-org-x-net-union.

* gnu/packages/syncthing.scm (go-golang-org-x-net-union): New variable.

gnu: Add go-github-com-vitrun-qart-union.

* gnu/packages/syncthing.scm (go-github-com-vitrun-qart-union): New variable.

gnu: Add go-github-com-gogo-protobuf-union.

* gnu/packages/syncthing.scm (go-github-com-gogo-protobuf-union): New variable.

gnu: Add go-golang-org-x-crypto-union.

* gnu/packages/syncthing.scm (go-golang-org-x-crypto-union): New variable.

gnu: Add go-github-com-audriusbutkevicius-kcp-go.

* gnu/packages/syncthing.scm (go-github-com-audriusbutkevicius-kcp-go): New
variable.

gnu: Add go-github-com-templexxx-reedsolomon.

* gnu/packages/syncthing.scm (go-github-com-templexxx-reedsolomon): New
variable.

gnu: Add go-github-com-templexxx-cpufeat.

* gnu/packages/syncthing.scm (go-github-com-templexxx-cpufeat): New variable.

gnu: Add go-github-com-kballard-go-shellquote.

* gnu/packages/syncthing.scm (go-github-com-kballard-go-shellquote): New
variable.

gnu: Add go-github-com-audriusbutkevicius-cli.

* gnu/packages/syncthing.scm (go-github-com-audriusbutkevicius-cli): New
variable.

gnu: Add go-golang-org-x-time-rate.

* gnu/packages/syncthing.scm (go-golang-org-x-time-rate): New variable.

gnu: Add go-github-com-xtaci-smux.

* gnu/packages/syncthing.scm (go-github-com-xtaci-smux): New variable.

gnu: Add go-github-com-pkg-errors.

* gnu/packages/syncthing.scm (go-github-com-pkg-errors): New variable.

gnu: Add go-github-com-templexxx-xor.

* gnu/packages/syncthing.scm (go-github-com-templexxx-xor): New variable.

gnu: Add go-github-com-chmduquesne-rollinghash-adler32.

* gnu/packages/syncthing.scm (go-github-com-chmduquesne-rollinghash-adler32):
New variable.

gnu: Add go-github-com-ccding-go-stun.

* gnu/packages/syncthing.scm (go-github-com-ccding-go-stun): New variable.

gnu: Add go-github-com-audriusbutkevicius-pfilter.

* gnu/packages/syncthing.scm (go-github-com-audriusbutkevicius-pfilter): New
variable.