INFR: Decide on a URL structure for custom URL

[mmcky]

Currently the

dp.quantecon.org

url is used to support the Dynamic Programming Book.

We have a few options:

• dp-lectures.quantecon.org
• use dp.quantecon.org and migrate the current website to book-dp.quantecon.org
• use dynamic-programming.quantecon.org

We could also look at starting a lecture series such as

• lecture.dp.quantecon.org

but that is starting to be a lot of unconventional dotting!