Update bundled Boost to fix recent-Linux compile errors

from 1.53 to 1.55

uintptr_t was undefined in some Boost headers.  Most likely
they'd been including some system headers that used to include
other system headers that define uintptr_t.  The new version of
Boost seems to have fixed this bug.
Merge branch 'fixes'
fix spelling
remove a set of old no-longer-relevant notes
Document how the source code is organized (in the README)
Merge github.com:Lasercake/Lasercake