Don't mess with new lines too much

[ewjoachim]

ping @tyoras

• When a secret doesn't contain a new line, it's probably good to strip it from all whitespace characters before saving it, and when displaying it with --text, we can add a trailing new line
• When a secret contains a newline (let's say it's a multi-line secret), we should not mess with it: no stripping input, and displaying as-is.

Need:

• There are tools that don't like multi-line secrets (a.k.a certs) that don't have a final new line.

[tyoras]

There is a workaround for the second case:

• if the multi-line secret looks like this:

line1
line2
line3

• make it a yaml file by wrapping the content like this:

---
|
  line1
  line2
  line3
...

• and finally it can be saved to the vault as a yaml that preserves the final newline:
  cat multi_line_secret.yml | vault set --yaml --stdin my_secret_key

[ewjoachim]

Closed by #118

(Ping if you want a release)