Add PRAGMA cipher_store_pass

PRAGMA cipher_store_pass allows the passphrase to remain in memory
which will allow an ATTACH statement to succeed without providing
the key value during ATTACH when both databases use the same passphrase,
but have different salt values.  Previously, in order to ATTACH with
this scneario, calling ATTACH required providing the key value inline.
fix redundant key derivation with common crypto provider
Adjust cipher version test
Converted readme to valid markdown
Fixed heading
Snapshot of upstream SQLite 3.8.6
Merge sqlite-release(3.8.6) into prerelease-integration
Remove extra block from merge
Bump cipher_version to 3.2.0
Change cipher_version test to match current version
Merge branch 'prerelease'
Merge pull request #1 from sqlcipher/master

sync