refactor: Use struct to parse API responses

- Return bytes for each request to the Flexpool API
- Delegate JSON marshalling the higher functions
- Use int64 when possible

BREAKING CHANGE: database structure has to be updated to use integer
instead of real. Please follow instructions to upgrade from 1.0 to 1.1.

Signed-off-by: Julien Riou <julien@riou.xyz>

migrations/1.0_to_1.1.sql

@@ -0,0 +1,49 @@
+-- Migrate from 1.0 to 1.1
+-- SQLite doesn't support ALTER TABLE... ALTER TYPE
+-- This migration file creates the new structures with "integer" types
+-- instead of "real", move data to this new table then drop the old one.
+
+-- miners
+
+ALTER TABLE `miners` RENAME TO `miners_old`;
+
+CREATE TABLE `miners` (
+    `id` integer,
+    `created_at` datetime,
+    `updated_at` datetime,
+    `deleted_at` datetime,
+    `coin` text,
+    `address` text NOT NULL UNIQUE,
+    `balance` integer,
+    `last_payment_timestamp` integer,
+    PRIMARY KEY (`id`)
+);
+
+INSERT INTO `miners` SELECT * FROM `miners_old`;
+
+DROP TABLE `miners_old`;
+
+CREATE INDEX `idx_miners_deleted_at` ON `miners`(`deleted_at`);
+
+
+-- pools
+
+ALTER TABLE `pools` RENAME TO `pools_old`;
+
+CREATE TABLE `pools` (
+    `id` integer,
+    `created_at` datetime,
+    `updated_at` datetime,
+    `deleted_at` datetime,
+    `coin` text NOT NULL UNIQUE,
+    `last_block_number` integer,
+    PRIMARY KEY (`id`)
+);
+
+INSERT INTO `pools` SELECT * FROM `pools_old`;
+
+DROP TABLE `pools_old`;
+
+CREATE INDEX `idx_pools_deleted_at` ON `pools`(`deleted_at`);
+
+SELECT "Database migrated to 1.1"