std::string buffer ctor

[yakra]

Problem with constructing a std::string from a raw char* is the computer doesn't immediately know how much space to allocate. It must either...

• Do a strlen or equivalent, and scan through the whole string, or
• Dynamically (re)allocate as it goes.

Both of which waste time. If we know in advance how much space will be needed, let's use this to our advantage.

• [ ] Waypoint ctor, label & AltLabel construction
• [ ] TravelerList ctor: orig_line & trim_line
• [ ] Wasn't there something in HighwaySystem::route_integrity?
• [ ] .list line fields
• [ ] Anywhere else?

[yakra]

Waypoint ctor, label & AltLabel construction

./check10.sh -h lab3 --null -v -e -r ReadWpt _clang _2long _buf

numthreads	_clang	_2long	_buf	_alt	_AInit
11	2.713	1.731	1.701	1.713	1.711
12	2.731	1.634	1.629	1.645	1.641
13	2.722	1.627	1.614	1.624	1.627
14	2.749	1.641	1.627	1.637	1.636

[yakra]

Dynamically (re)allocate as it goes.

This appears to be what happens in any case. Creating an 11-char string with all the constructors yields a 15-char capacity, every time, in both g++ and clang++. Capacity doubles whenever more is needed. Not much harm comes from this; almost all route names & labels are well below this threshold. Standard OSM URLs with 6 decimal places top out right at 60 B, and will only need to reallocate twice. Worse than nothing, but hey.

Performance appears to be marginally worse, right at margin of error.