[HIVEMALL-193] Implement a tool for generating a list of Hivemall UDFs

[takuti]

What changes were proposed in this pull request?

Automatically generate a list of UDFs for:

• https://hivemall.incubator.apache.org/userguide/misc/funcs.html
• https://hivemall.incubator.apache.org/userguide/misc/generic_funcs.html

Initial mock implementation: https://github.com/takuti/hivemalldoc

What type of PR is it?

Improvement, Documentation

What is the Jira issue?

https://issues.apache.org/jira/browse/HIVEMALL-193

How was this patch tested?

See output: https://gist.github.com/takuti/312d3a11bf85fc4044399d7e97a06f13

How to use this feature?

$ mvn clean package -Dskiptests=true -Dmaven.test.skip=true
$ mvn org.apache.hivemall:hivemall-docs:generate-funcs-list

Checklist

• Did you apply source code formatter, i.e., mvn formatter:format, for your commit?

[myui]

Instead of using shaded jar, it's better to use MOJO.

Goals such as mvn hivemall-docs:gen_func_list.

[takuti]

fb81564

Usage:

$ mvn org.apache.hivemall:hivemall-docs:generate-funcs-list

Lists of UDFs are written into target/funcs.md and target/generic_funcs.md

[myui]

@takuti Why not directly update these files?

docs/gitbook/misc/funcs.md
docs/gitbook/misc/generic_funcs.md

[takuti]

Just in case, the generator defensively does so. If you feel directly over-writing docs/gitbook/* is fine, I can update so.

[myui]

I prefer directly updating them since it's intendedly updated by running mvn org.apache.hivemall:hivemall-docs:generate-funcs-list.

If you are using git, there are no problem for undo.

[takuti]

Now mvn org.apache.hivemall:hivemall-docs:generate-funcs-list automatically updates docs/gitbook/*

[myui]

LGTM. Merged! Thanks.