[learn] Using WAL as the journal mode while learning
[learn] Using WAL as the journal mode while learning

Before this commit, learn-from-file was using MEMORY as the journal
mode. This was locking the whole database making read and write blocked
till the learn-from file finishes.

From this commit onwards, we use WAL mode so that learn and
transliteration can continue together.

varnamproject/libvarnam,varnamproject/libvarnam,varnamproject/libvarnam