Updated Structure of the code (markdown)

Structure-of-the-code.md

@@ -7,6 +7,7 @@ osxphotos is built around a set of classes that each handle a particular aspect
 * FolderInfo: represents a folder in the library.
 * PlaceInfo: represents the reverse geolocation info (e.g. the address or place name) associated with a photo.
 * ExifTool: provides an interface to the [exiftool](https://exiftool.org/) tool for manipulating EXIF information associated with a photo.
+* PhotoTemplate: helper class for rendering a template string.
 
 The package code is organized in osxphotos per the table below. Most of the files contain doc strings describing what they contain. 
 
@@ -23,8 +24,9 @@ The package code is organized in osxphotos per the table below. Most of the file
 |`exiftool.py`|              ExifTool class|
 |`photoinfo/`|             PhotoInfo class|
 |`photosdb/`|              PhotosDB class|
+|`phototemplate.py`|       PhotoTemplate class|
 |`placeinfo.py`|             PlaceInfo class|
-|`templates`|                contains [mako](https://www.makotemplates.org/) templates for sidecar export (though the name is similar, these templates are not associated with `templates.py`|
+|`templates`|                contains [mako](https://www.makotemplates.org/) templates for sidecar export (though the name is similar, these templates are not associated with `phototemplate.py`|
 |`templates/xmp_sidecar.mako`|mako template used to create [XMP](https://en.wikipedia.org/wiki/Extensible_Metadata_Platform) sidecar files|
 |`utils.py`|                 various utility methods--this file is getting bloated and needs to be refactored|
 
@@ -43,7 +45,7 @@ As an example, here's a rough outline of what you'd need to do to add support fo
 1. Reverse engineer Photos.sqlite and develop an sql query that extracts the data
 2. Add this query to `PhotosDB._process_database5` (assuming a Photos 5 library) and store the data in appropriate data structure accessible through `_dbphotos`
 3. Add a property to `PhotoInfo` which accesses `_dbphotos` through `self._db` which points to the PhotosDB object.  If your change requires significant code, consider creating a separate file for the method -- see _photoinfo_export.py for an example
-4. If exposing the property to the templating system (`PhotoInfo.render_template()`) and add it to `templates.py` (which is relatively self-documenting)
+4. If exposing the property to the templating system (`PhotoTemplate` and `PhotoInfo.render_template()`) add it to `phototemplate.py` (which is relatively self-documenting)
 5. If exposing the property to the command line interface, add it to `__main__.py` -- you'll want to look at `query_options`, `_query()`, `export()`, and `export_photo()` at a minimum to ensure the command line tool can access your new attribute. 
 6. Add at least one test to `tests/`!
 7. Ensure all tests pass `python3 -m pytest tests/`