fix doc warnings/errors

warnings that have been fixed

```
changelog.rst:659: WARNING: Inline interpreted text or phrase reference start-string without end-string.
errors.rst:35: WARNING: duplicate object description of show_error, other instance in common_functions.rst
errors.rst:58: WARNING: duplicate object description of show_404, other instance in common_functions.rst
errors.rst:80: WARNING: duplicate object description of log_message, other instance in common_functions.rst
calendar.rst:93: ERROR: Malformed table. Text in column margin in table line 5.
```

changes I did
- Remove 's from `<database/query_builder>` to prevent miss-interpretation
- Added `:noindex:` to functions that are defined in multiple places, which causes them to directly link to original function location
- Fix spacing in table to prevent malformed table warning