Added trim to available methods in template

[mariusGundersen]

it simply removes whitespace from the given string.

[jwilder]

Thanks @mariusGundersen!

[md5]

I ran into a problem with this in nginx-proxy/nginx-proxy@f394596

Since strings.TrimSpace strictly takes a string, it barfs if it gets passed an interface{}, even if it's actually a string.

I think it would be worthwhile to have some sort of stringToStringHelper function to use internally in docker-gen to take functions that are func(string) string and turn them into func(interface {}) string using reflection to check if the argument is actually a string or a *string. I could also see having other helpers like stringStringToStringHelper for the func(string,string) string case (and possibly others).

[jwilder]

Maybe all the template functions should just work with interface{} and return the original value if it's not a string?

[md5]

I think they should probably error out when they aren't given what they expect, but I think in general it's good for the functions to be flexible in the concrete types they accept as long as the reflected types are usable.

[jwilder]

Agreed. Looks like hugo does that for its functions: https://github.com/spf13/hugo/blob/master/tpl/template_funcs.go

[md5]

spf13/cast looks quite useful 👍