Wrapping strategies for function calls

[vitiral]

I would like to define the formatting strategy for function calls. It does not currently exist in the style guide

Basic idea

Method 1:

very_long_module_name::this_is_a_really_long_function(arg1,
                                                      arg2,
                                                      arg3,
                                                      "this is a raw s\
                                                       tring and is ter\
                                                       ible")

should instead be Method 2:

very_long_module_name::this_is_a_really_long_function(
    arg1, arg2, arg3, 
    "this is a raw string and is terible")

rustfmt currently uses the Method 1 way too often. I'm not sure the right balance here. Like @joshtriplett said in #47 , you really want to define "simple". IMO "simple" would be:

• If the function and all args fit within the line length, just do that.
• Otherwise use Method 1 if Method 1 only takes up two lines
• Otherwise use Method 2:
  • arguments always start on their own indented line
  • arguments are listed normally as long as they don't go over the line length limit
  • any argument that would go over the line length limit goes on it's own line
  • anything over 25 characters goes on it's own line

[nrc]

Dup of #65