SDK-261 AS documentation generated by hydra should use URLs hosted by hydra

[matthewhammer]

Originally, I had put URLs into the code that point at github. Now, we have static URLs hosted on hydra. Also, we have recently merged into master.

To make the generated documentation consistent with these changes, I still need to do a few things:

• use the correct base URL; we likely want to use master for this URL, consistently
• use the correct file names, with the correct extensions; these used to be .md but are now .html; this requires a lot of small, simple changes in a lot of files.

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Some example doc links (note that they each refer to master, not the current state of this PR):

• stdlib documentation hosted on hydra
• PX documentation hosted on hydra