go vet and lint

* Naming
    * If this is not some OpenPGP standard I follow rule that `DES` should be
      upper case as it is abreviation and `Triple` should be camel-case as it
      is normal word hence `TripleDES`
    * rename `errors2` -> `errorsPGP`
* long lines
    * https://github.com/golang/go/wiki/CodeReviewComments#line-length
    * I bit improved long lines based on my folding
    * reuse type in definition if possible i.e. `a string, b string, c string` -> `a,b,c string`
    * `if long_statetent(); err!=nil {` -> `long_statement;↵ if err!=nil {`
    * spaces around operators (e.g. `a + b` -> `a+b`)
* removing empty lines on start and end of scope
* comments
    * on all exported functions
    * start with function name
* import:
    * order in alphabet
    * separate native, golang.org/x/ and our libs

constants/cipher.go

@@ -0,0 +1,11 @@
+package constants
+
+// Definitions for cipher suites
+const (
+	ThreeDES  = "3des"
+	TripleDES = "tripledes"
+	CAST5     = "cast5"
+	AES128    = "aes128"
+	AES192    = "aes192"
+	AES256    = "aes256"
+)