Go treats underscores specially

In case there's ever a platform called helpers or protocol, we don't
want to be doing this.

diff --git a/noise_helpers.go b/noise-helpers.go
similarity index 100%
rename from noise_helpers.go
rename to noise-helpers.go

diff --git a/noise_protocol.go b/noise-protocol.go
similarity index 100%
rename from noise_protocol.go
rename to noise-protocol.go

diff --git a/noise_types.go b/noise-types.go
similarity index 100%
rename from noise_types.go
rename to noise-types.go