Makefile: Build new 'snabblite' binary in addition to 'snabbswitch'.

snabblite does not have the Lua code linked so it's loaded from disk
instead. This means a couple of things:
- LuaJIT seems to give better error messages for code loaded from source.
- LuaJIT seems to work better with linux perftools when loading form source.
- Lua sources can be changed and tested without recompiling.

Going forward perhaps linking source rather than bytecode in
snabbswitch will be best if indeed bytecode gives worse debug info.
New function: memory.map(virtual_address) => physical_address
Works for all addresses in the snabbswitch process. How cool is that?

Implemented using Linux /proc/self/pagemap feature.

The memory module includes a selftest function:

selftest: physmem
50e5d000:10000000 are the virtual:physical base addresses.
Testing mapping with random addresses:
51b1211b:10cb511b 5198b7ff:10b2e7ff 517ce10a:1097110a 51a6a397:10c0d397
50fa8a88:1014ba88 518f0e52:10a93e52 513cae8e:1056de8e 51a22965:10bc5965
51530b59:106d3b59 51775f44:10918f44 51031d60:101d4d60 50f3dd74:100e0d74
51df32be:10f962be 519a64fd:10b494fd 5112db95:102d0b95 51df5c76:10f98c76
512cb57d:1046e57d 51407628:105aa628 515ebcd5:1078ecd5 5193a344:10add344
51790c7e:10933c7e 51b1d3a5:10cc03a5 5159756f:1073a56f 511468da:102e98da
518ec562:10a8f562 511bdf5c:10360f5c 517e92e0:1098c2e0 510ab48b:1024e48b
51ba453b:10d4753b 517b2389:10955389 50ec28e4:100658e4 51bbee91:10d61e91
50f28334:100cb334 51ba2f37:10d45f37 518632d9:10a062d9 51b975e7:10d3a5e7
511415c8:102e45c8 51273791:10416791 51d1a051:10ebd051 5136f4a4:105124a4
50f9ec3a:10141c3a 5140a769:105ad769 51d196ba:10ebc6ba 50ec38bc:100668bc
51931aab:10ad4aab 51a468b7:10be98b7 517374d8:108da4d8 5103f6d4:101e26d4
5108022a:1022322a 50ee4d6e:10087d6e 5165a254:107fd254 5196448f:10b0748f
51677cf4:1081acf4 51c0d5ab:10db05ab 510988e3:1023b8e3 5130d5c6:104b05c6
51c67592:10e0a592 51a9c778:10c3f778 5197e118:10b21118 518bf3d4:10a623d4
51bc8f2e:10d6bf2e 50e87fc3:1002afc3 50f39f07:100dcf07 51aab258:10c4e258
OK