[FR] Add a command to automatically create sections for each header.

[XMB-7]

# h1
xxx

## h2
xxx

# another h1
xxx

->

%%SECTION{h1}%%
# h1
xxx

%%SECTION{h1 > h2}%%
## h2
xxx

%%SECTION{another h1}%%
# another h1
xxx

It's just a rough idea, and I believe various details may be concerned, like switching the display format of %%SECTION{...}%% from a divider line to something else, whether only applies to L1 level headers, auto-trimming section names or not...