support multiple input files

[cldellow]

Fixes #696, a regression introduced in the v3.0 work:

• fix bug in thread locals for generate_stream and generate_output
  • if the thread local was read on the main thread, we would previously fail to reset it for the subsequent PBF file
• use the old NodeStore/WayStore when multiple input files are present
  • the optimization for Sort.Type_then_ID assumes IDs are monotonically increasing. This is not true when there are multiple PBFs, as the subsequent PBF restarts its numbering.
• don't use lazy geometries when multiple input files present
  • LeasedStore assumed that there would be at most 1 PBF being read. This might be fixable by multiplying threadNum by the number of PBFs to be read in the initializers here:

    tilemaker/src/tile_data.cpp

    Lines 54 to 57 in 07e878f

    	pointStores(threadNum),
    	linestringStores(threadNum),
    	multilinestringStores(threadNum),
    	multipolygonStores(threadNum),

• compute the bbox from the union of all the pbfs
  • I think this may have been a pre-existing bug, made more noticeable by changes in v3 that relied more heavily on the bbox being correct

For testing, I built a pmtiles with monaco + liechtenstein and verified they both showed up.

I think we could probably support lazy geometries, but have left it alone for now.

[systemed]

Thanks! Tested with Oxfordshire+Worcestershire+Gloucestershire and works well. (I'd had a brief look previously and spotted the thread local issue but not the others.)