Fix grammar's indent and misc.

source/macros.tex:
	Add \noindent to environment bnfbase in order to fix indent.
	Add newcommand \contextdependentkeyword to environment bnfbase for
	indexing context-dependent keywords.
source/lex.tex:
	Transpose an order of \begin{bnf} and \indextext so that \indextext
	is not extracted by tools/makegram.
tools/grambase.tex:
	Use \contextdependentkeyword for indexing.
	Add \end{bnf} and \begin{bnf} between each element.
tools/makegram:
	Remove gramb.sed because it adds an unnecessary blank line.
tools/gramb.sed:
	Remove.
source/grammar.tex:
	Reflect changes above.