lint: ensure conformity with asmfmt

Run asmfmt suring linting and confirm git repository isn't dirty.
This introduces a developer tools dependency on asmfmt, but not a
runtime dependency.

Updates #8

script/bootstrap

@@ -14,3 +14,6 @@ go get -u github.com/campoy/embedmd
 
 # covertool for merging coverage reports
 go get -u github.com/dlespiau/covertool
+
+# asmfmt for enforcing assembly style
+go get -u github.com/klauspost/asmfmt