Handle indentation

[fangpenlin]

According to feedback posted by Dan in Beancount's Google group, it seems like this parser cannot handle

• Assets:Section:With:Funny:Name
  and this:
  2022-04-10 * "Test"
• Assets:Posting:With:Flag

or between this two metadata entries:

2022-04-10 * "Test"
transaction-metadata: 42
Assets:Tests 1 TEST
posting:metadata: 25

?

I gave it a quick try via the online formatter and the posting flag is
interpreted as an org-mode heading and posting metadata entries are not
supported.

I haven't find a time to try this out, but will look into it see how to address the indentation corner case