style: improve formatting of string concatenation

[ee7]

The lack of spaces around & here made these harder to read.

My first reading of:

&"

is the beginning of a strformat format string, like:

import std/strformat

const msg = "hello"
doAssert &"{msg}\n" == "hello\n"

Let's write:

& "

to clarify that we're doing string concatenation.

Also reformat a little and change .toLower to .toLower() while we're here, since using parens to distinguish calls from field accesses seems to be our style.

[ee7]

Ping @miki725 - could you review? A trivial style-only change that's been sitting for a while - I'd like to reduce the number of open PRs in nimutils.

We can consider formatting the code later when it won't cause merge conflicts for people, but let's just merge this since (I guess) it bothered me enough to create it.

[miki725]

Great. All of these came from third party library which had some wonky formatting...