R: updated manual pages, 'synopsis' section is not allowed any more.
Get rid of references to stderr, stdout and exit, these are not allowed in the R package.

Conflicts:

	src/foreign-dl-lexer.l
	src/foreign-gml-lexer.l
	src/foreign-lgl-lexer.l
	src/foreign-ncol-lexer.l
	src/foreign-pajek-lexer.l
Added igraph_warningf() for 'develop', we need this for some messages that replace exit in the parsers.
R: removed unneeded LICENSE file.