added plugins

plugins/dbgate-plugin-excel/README.md

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+
+# dbgate-plugin-excel
+
+MS Excel import/export plugin for DbGate
+
+
+## Usage without DbGate
+
+Export from fake object reader into MS Excel file. Fake object file can be replaced with other reader/writer factory functions, as described in 
+[dbgate-api package](https://www.npmjs.com/package/dbgate-api)
+
+```javascript
+const dbgateApi = require('dbgate-api');
+const dbgatePluginExcel = require("dbgate-plugin-excel");
+
+dbgateApi.registerPlugins(dbgatePluginExcel);
+
+
+async function run() {
+  const reader = await dbgateApi.fakeObjectReader();
+  const writer = await dbgatePluginExcel.shellApi.writer({ fileName: 'myfile1.xlsx', sheetName: 'Sheet 1' });
+  await dbgateApi.copyStream(reader, writer);
+  console.log('Finished job script');
+}
+dbgateApi.runScript(run);
+
+
+```
+
+## Factory functions
+
+### shellApi.reader
+Reads tabular data from one sheet in MS Excel file.
+```js
+  const reader = await dbgatePluginExcel.shellApi.reader({
+    fileName: 'test.xlsx',
+    sheetName: 'Album',
+    limitRows: null
+  });
+```
+
+### shellApi.writer
+Writes tabular data into MS excel file. There could be more writes into the some file in one script, if property sheetName is different.
+```js
+  const reader = await dbgatePluginExcel.shellApi.writer({
+    fileName: 'test.xlsx',
+    sheetName: 'Album',
+  });
+```