create data type builder in memory, todo: save to disk & load from disk
implment load/save data type definition
fix one potential memory leak. make header file cleaner
remove unnecessary unique_ptr wrap.
add test for pagerank
fix pagerank build on mac
Merge pull request #60 from thinxer/pr_test

add test for pagerank
Merge branch 'field-meta-info' of github.com:pondering/saedb into merge-field

Conflicts:
	src/saedb/io/CMakeLists.txt