lex.go: Add isStartOfLine()
lex_test.go: Improve error output message
Rename test section test 002
parse.go: Rewrite peek()

Previously peek() did not properly handle the token buffer. tokenPeekCount was
incremented needlessly without first checking the token buffer if there was an
item already retrieved from the lexer.
parse.go: Move skip() back into next()
parse.go: Add peekSkip()
Implement section test 008

Section title overlines a rewrite of t.section().