A B*-Tree implementation.

This is a simple, educational B*-Tree implementation based on B+-Tree, not B-Tree.
C-style, not STL.

• insert with preemptive split
• erase with preemptive merge
• find
• Range query
• Cpp-style

NO DUPLICATED KEY ORIGINALLY SUPPORTED,
but val_type can be a std::vector or some container else.

Lack of error handling.

$ g++ -O2 ./bstar_tester.cpp  -o ./_output.run && ./_output.run

std::map insert
std::map find
test output 49999995000000
std::map erase
Insert time: 8.04212 s
Erase time:  7.31826 s
Find time:  8.52046 s
B-star insert
B-star find
test output 49999995000000
B-star erase
Insert time: 3.01029 s
Erase time:  2.92722 s
Find time:  2.77145 s