Convert into a constexpr unordered_map

[amallia]

pisa/include/index_types.hpp

Lines 50 to 56 in c421f3d

	#define DS2I_INDEX_TYPES \
	(ef)(single)(uniform)(opt)(block_optpfor)(block_varintg8iu)(block_streamvbyte)( \
	block_maskedvbyte)(block_interpolative)(block_qmx)(block_varintgb)(block_simple8b)( \
	block_simple16)(block_simdbp)(block_mixed)
	#define DS2I_BLOCK_INDEX_TYPES \
	(block_optpfor)(block_varintg8iu)(block_streamvbyte)(block_maskedvbyte)(block_interpolative)( \
	block_qmx)(block_varintgb)(block_simple8b)(block_simple16)(block_simdbp)(block_mixed)

This can be converted into a constexpr map, s.t. the following can be implemented with a table lookup.

pisa/benchmarks/selective_queries.cpp

Lines 67 to 78 in 8177a47

	if (false) {
	#define LOOP_BODY(R, DATA, T) \
	} else if (type == BOOST_PP_STRINGIZE(T)) { \
	selective_queries<BOOST_PP_CAT(T, _index)> \
	(index_filename, type);
	/**/
	BOOST_PP_SEQ_FOR_EACH(LOOP_BODY, _, DS2I_INDEX_TYPES);
	#undef LOOP_BODY
	} else {
	logger() << "ERROR: Unknown type " << type << std::endl;
	}

[amallia]

We could use https://github.com/serge-sans-paille/frozen here.