Add StringArray

[ufrhaidar]

useful sometimes.

Feels dumb to do that in local workspace, so hide it in common_interfaces.

[fujitatomoya]

i thought this sounds reasonable at 1st, but std_msgs does not have any array typed messages at all but MultiArray. i think this is intention to keep it in that way?

@tfoote @clalancette what do you think?

[ufrhaidar]

I originally just wanted to add an array of StringArrays to a custom message. Was hoping someone would suggest a better way to achieve that like string[][] 😂

Looks like it can be added to example_msgs like the rest.

[fujitatomoya]

We had a discussion in PMC meeting. This is probably not gonna be taken, we try to keep the primitive types only. thank you very much for opening PR and idea.

[ufrhaidar]

any reconsideration after #262 ?

[tfoote]

That one has semantic information beyond an array of primatives. This does not. I'm asking for a rereview of that one before it's released though.