Implement human-friendly notation of highlight and indentation

for debugging and assertion
Implement Minitest::Assertions.assert_parse

Partly rewrite test/test_erm_buffer.rb using assert_parse
Fix `require 'strscan'`
Remove unnecessary condition
Use chevrons for delimiters
Fix regexp

to remove newlines only on the head or tail of strings
Rewrite the rest of test/test_erm_buffer.rb

with assert_parse
Fix style
Clarify a variable name
Merge pull request #55 from vzvu3k6k/xml-like-notation

Human-friendly highlight and indentation notation for debugging and testing