The hand-written number parser functions implemented using strtod and
friends were rather slow (profiling indicates that typically 30% of the
program is spent inside of strtod internals). By using
boost::spirit::qi, which we already depend on through boost-filesystem
and others this portion typically seem to be reduced to 20% (via
instruction count) and with somewhat better cache performance.
Rudimentary measuring indicates ~15% speedup overall.
Additionally, the intention is a lot clearer this way, so readability
received a boost. Compilation time of StarToken goes through the roof.
d9443c7355