Support slice types

[iahmedov]

This fixes bug related to parsing values given as array. traefik/traefik#2416

Chose CSV parser, because it has better handling of comma separated values including consideration of quotation mark.

1,2,3 -> 
- 1
- 2
- 3

word, "quoted", "quoted and comma," -> 
- word
- quoted
- quoted and comma,

[coveralls]

Coverage increased (+0.6%) to 80.965% when pulling a6f3a5b on iahmedov:array_support into af517d5 on containous:master.