Add comprehensive documentation with i18n support (EN/BG)

- Add docs/ folder with English (en/) and Bulgarian (bg/) documentation
- Create index.md with language switching and links
- English docs: installation, quickstart, architecture, baraql, storage,
  schema, lsm, btree, vector, graph, fts, columnar, transactions,
  distributed, protocol, udf, api-binary, api-http, api-websocket
- Bulgarian docs: installation, quickstart, architecture, baraql,
  schema, lsm, btree, vector, graph, fts, transactions, distributed
- Update README license to BSD 3-Clause
- Add LICENSE file with BSD 3-Clause text

docs/bg/lsm.md

@@ -0,0 +1,25 @@
+# LSM-Tree Съхранение
+
+Основният двигател за съхранение използващ Log-Structured Merge-Tree архитектура.
+
+## Употреба
+
+```nim
+import barabadb/storage/lsm
+
+var db = newLSMTree("./data")
+
+db.put("key1", cast[seq[byte]]("value1"))
+let (found, value) = db.get("key1")
+
+db.close()
+```
+
+## Компоненти
+
+- **MemTable**: Сортиран буфер в паметта
+- **WAL**: Write-ahead log за трайност
+- **SSTable**: Сортирани таблици на диска
+- **Bloom Filter**: Бързи негативни проверки
+- **Compaction**: Сливане на SSTables
+- **Page Cache**: LRU кеш