Add GitHub Issue and Pull Request Templates

[bflad]

Will fix the TravisCI issue separately (and move this repository to GitHub Actions):

$ make tools
GO111MODULE=off go get -u github.com/golangci/golangci-lint/cmd/golangci-lint
# github.com/golangci/golangci-lint/pkg/golinters
../../golangci/golangci-lint/pkg/golinters/golint.go:21:14: l.LintPkg undefined (type *"github.com/golangci/lint-1".Linter has no field or method LintPkg)
../../golangci/golangci-lint/pkg/golinters/gomnd.go:13:6: cannot use magic_numbers.Analyzer (type *"github.com/tommy-muehle/go-mnd/vendor/golang.org/x/tools/go/analysis".Analyzer) as type *"golang.org/x/tools/go/analysis".Analyzer in array or slice literal
../../golangci/golangci-lint/pkg/golinters/unused.go:16:7: undefined: unused.NewChecker
GNUmakefile:15: recipe for target 'tools' failed
make: *** [tools] Error 2
The command "make tools" failed and exited with 2 during .

[anGie44]

LGTM 👍