Add experimental postgres backend to GitRekt.Git

See #2 for more details.

apps/gitgud/priv/db/migrations/20190411211844_add_git_objects_table.exs

@@ -0,0 +1,13 @@
+defmodule GitGud.DB.Migrations.AddGitObjectsTable do
+  use Ecto.Migration
+
+  def change do
+    create table("git_objects", primary_key: false) do
+      add :oid, :binary, primary_key: true
+      add :repo_id, references("repositories", on_delete: :delete_all), primary_key: true
+      add :type, :integer, null: false
+      add :size, :integer, null: false
+      add :data, :binary
+    end
+  end
+end

apps/gitgud/priv/db/migrations/20190411212320_add_git_references_table.exs

@@ -0,0 +1,12 @@
+defmodule GitGud.DB.Migrations.AddGitReferencesTable do
+  use Ecto.Migration
+
+  def change do
+    create table("git_references", primary_key: false) do
+      add :name, :string, primary_key: true
+      add :repo_id, references("repositories", on_delete: :delete_all), primary_key: true
+      add :symlink, :string
+      add :oid, :binary
+    end
+  end
+end

apps/gitrekt/Makefile

@@ -1,6 +1,6 @@
 ERLANG_PATH ?= $(shell erl -eval 'io:format("~s", [lists:concat([code:root_dir(), "/erts-", erlang:system_info(version), "/include"])])' -s init stop -noshell)
 CFLAGS  	?= -O2 -Wall -Wextra -Wno-unused-parameter -I$(ERLANG_PATH)
-LDFLAGS 	+= -lgit2
+LDFLAGS 	+= -lgit2 -lpq
 
 ifneq ($(OS),Windows_NT)
 	CFLAGS += -fPIC

apps/gitrekt/c_src/geef.c

@@ -216,6 +216,7 @@ static ErlNifFunc geef_funcs[] =
 {
 	{"repository_init", 2, geef_repository_init, 0},
 	{"repository_open", 1, geef_repository_open, 0},
+	{"repository_open_postgres", 2, geef_repository_open_postgres, 0},
 	{"repository_discover", 1, geef_repository_discover, 0},
 	{"repository_bare?", 1, geef_repository_is_bare, 0},
 	{"repository_empty?", 1, geef_repository_is_empty, 0},