Be smarter about trimming whitespace when creating records from ASCII

[ahupowerdns]

In ff7ac44 we added trimming of whitespace,
so you could turn " 1.2.3.4 " into an A record 0x01020304. This commit made us more flexible
but also six times slower in some microbenchmarks.

This commit restores the old performance which shaves double digits percentages of time from many
benchmarks in 'speedtest', while making "make-a record" six times faster again.

Short description

Checklist

I have:

• read the CONTRIBUTING.md document
• compiled this code
• tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)
• checked that this code was merged to master