Handle events

- Adds interfaces for developers to build handlers that update data in
response to log events
- Resolves #29

pkg/datastore/inmemory/in_memory.go

@@ -0,0 +1,30 @@
+package inmemory
+
+import (
+	"github.com/vulcanize/vulcanizedb/pkg/core"
+	"github.com/vulcanize/vulcanizedb/pkg/filters"
+)
+
+const (
+	blocksFromHeadBeforeFinal = 20
+)
+
+type InMemory struct {
+	blocks                       map[int64]core.Block
+	receipts                     map[string]core.Receipt
+	contracts                    map[string]core.Contract
+	logs                         map[string][]core.Log
+	logFilters                   map[string]filters.LogFilter
+	CreateOrUpdateBlockCallCount int
+}
+
+func NewInMemory() *InMemory {
+	return &InMemory{
+		CreateOrUpdateBlockCallCount: 0,
+		blocks:     make(map[int64]core.Block),
+		receipts:   make(map[string]core.Receipt),
+		contracts:  make(map[string]core.Contract),
+		logs:       make(map[string][]core.Log),
+		logFilters: make(map[string]filters.LogFilter),
+	}
+}