WIP: [schema] Adding Schema module

[gullitmiranda]

Discussion: #30

TODO:

• Add tests
• Add macro Connection.insert/2 ([proposal] Series struct like Ecto.Schema #30 (comment))
• Add macro Connection.all/2([proposal] Series struct like Ecto.Schema #30 (comment))

[coveralls]

Coverage decreased (-0.6%) to 98.16% when pulling 54e9b50 on gullitmiranda:feature/schema into c2e8bc3 on mneudert:master.

[coveralls]

Coverage decreased (-0.6%) to 98.16% when pulling 9015bda on gullitmiranda:feature/schema into c2e8bc3 on mneudert:master.

[coveralls]

Coverage decreased (-0.6%) to 98.16% when pulling 086bd63 on gullitmiranda:feature/schema into c2e8bc3 on mneudert:master.