Only check for non-empty value when storing data
Increase key size
Do not use magic constants
Improve compress() a bit
Add missing NUL terminator after compress
Fix compressing same value as a key
Compute number of inserts properly

Even when not printing progress, count the number of strings inserted
into the trie.
Automatize the test better
Deduplicate stored data

Only store one copy of each string associated with any key. Before
serializing the data, an ordered index is created with only one copy of
each string. This allows for very fast lookup of the string.
Simplify deduplication function
Add more assertions
Move string index creation to separate function
Allocate all data memory at once
Simplify storing data