Refactor and improve the timew-config.7 man page

Refactor and improve the [config (7)](https://timewarrior.net/reference/timew-config.7/) man page:
a. Break existing Description into subsections on file content, file location, and migration.
b. Define syntax of configuration directives: = . (I wasn't sure if the "=" syntax was required, or whether should be quoted).
c. Explain comment syntax.
d. Mention include directive (if that is supported; I see it in [Rules.cpp](https://github.com/GothenburgBitFactory/timewarrior/blob/develop/src/Rules.cpp) code but I don't recall reading it in documentation).
e. Explain that hint values are not preceded by colon characters.
f. State the rules for interpreting "yes" and "no" values.
g. State the relationship between using config settings in this file and using the same setting in a command invocation.
h. Reword the Configuration section to clarify that it lists a few of the possible configuration names available, but not all. Right now this section appears to imply that it describes how to configure the config(7) file, which is not really correct.