Support loading extensions (closes #136)

[mindreframer]

As initial selection for SQLITE extensions we take https://github.com/nalgeon/sqlean with some additions in this fork (https://github.com/mindreframer/sqlean) + packaged as Hex package here: https://hex.pm/packages/ex_sqlean.

To keep the usage for Exqlite somewhat simpler and consistent, a new module is introduced: BasicAPI. It allows simple operations without the confusion between Exqlite.Sqlite3 and Exqlite.Connection modules to execute queries and dealing with results.

[mindreframer]

@warmwaffles @kevinlang @cw789 Ping?

[warmwaffles]

@mindreframer I've never actually loaded extensions before. Do you have to unload them before you close the sqlite connection?

[mindreframer]

@warmwaffles I don't think so. Just closing SQLite connection is enough. An extension is loaded in the context of a connection and does not linger around / or leak to other connections.

[mindreframer]

@warmwaffles Feel free to play around and suggest some further improvements. I'm not a C programmer, so I kinda copy-pasted the NIF code together, and worked around the booleans by mapping them to 1/0 in the sqlite3.ex file. It might not be 100% bullet proof, but got the job done.

[warmwaffles]

The C code looks completely fine.

[cw789]

@cw789 Ping?

Thanks for asking. But I think I could not help much regarding this.
OTP 21+ is also fine in my opinion.

If you really ask me, I think I would miss how I could use SQLean or other Plugins (if others exists).
A little bit of docs? ;)

[mindreframer]

@cw789 Thanks for the feedback! I have added a section in the Readme with some code snippets about how to use SQLean extensions.

[mindreframer]

@warmwaffles thanks for merging!

[cw789]

Thanks for making.

[warmwaffles]

No problem. I was eyeballing sqlean a while back but decided against incorporating it into this library. Having it as an external is totally fine.