Add CI fixes and improvements (#780)

* Update GolangCI-lint and lint config

The `algo` parameter for the `unparam` linter has been removed and we
should thus no longer specify it. Also, bumping the GolangCI-lint
version to the latest available minor release.

See: mvdan/unparam@e6a6d1c51b

* Fix and improve bintray CI script

* Further CI setup improvements

* Split-out CI steps into stand-alone scripts

.golangci.yaml

@@ -7,7 +7,7 @@ run:
   # concurrency: 4
 
   # timeout for analysis, e.g. 30s, 5m, default is 1m
-  deadline: 1m
+  deadline: 2m
 
   # exit code when at least one issue was found, default is 1
   issues-exit-code: 1
@@ -105,10 +105,6 @@ linters-settings:
     # with golangci-lint call it on a directory with the changed file.
     check-exported: false
   unparam:
-    # call graph construction algorithm (cha, rta). In general, use cha for libraries,
-    # and rta for programs with main packages. Default is cha.
-    algo: rta
-
     # Inspect exported functions, default is false. Set to true if no external program/library imports your code.
     # XXX: if you enable this setting, unparam will report a lot of false-positives in text editors:
     # if it's called for subdir of a project it can't find external interfaces. All text editor integrations