### What changes were proposed in this pull request?
This PR replaces the non-ASCII characters to ASCII characters when possible in PySpark documentation
### Why are the changes needed?
To avoid unnecessarily using other non-ASCII characters which could lead to the issue such as https://github.com/apache/spark/pull/32047 or https://github.com/apache/spark/pull/22782
### Does this PR introduce _any_ user-facing change?
Virtually no.
### How was this patch tested?
Found via (Mac OS):
```bash
# In Spark root directory
cd python
pcregrep --color='auto' -n "[\x80-\xFF]" `git ls-files .`
```
Closes#32048 from HyukjinKwon/minor-fix.
Authored-by: HyukjinKwon <gurwls223@apache.org>
Signed-off-by: Max Gekk <max.gekk@gmail.com>
### What changes were proposed in this pull request?
This PR is a minor followup to fix:
1. Slightly reword the wording in the main page.
2. The indentation in the table at the migration guide;
from
to
### Why are the changes needed?
In order to show the migration guide pretty.
### Does this PR introduce _any_ user-facing change?
Yes, this is a change to user-facing documentation.
### How was this patch tested?
Manually built the documentation.
Closes#29606 from HyukjinKwon/SPARK-32191.
Authored-by: HyukjinKwon <gurwls223@apache.org>
Signed-off-by: HyukjinKwon <gurwls223@apache.org>
### What changes were proposed in this pull request?
This proposes to port old PySpark migration guide to new PySpark docs.
### Why are the changes needed?
Better documentation.
### Does this PR introduce _any_ user-facing change?
No. Documentation only.
### How was this patch tested?
Generated document locally.
<img width="1521" alt="Screen Shot 2020-08-07 at 1 53 20 PM" src="https://user-images.githubusercontent.com/68855/89687618-672e7700-d8b5-11ea-8f29-67a9ab271fa8.png">
Closes#29385 from viirya/SPARK-32191.
Authored-by: Liang-Chi Hsieh <viirya@gmail.com>
Signed-off-by: HyukjinKwon <gurwls223@apache.org>
