lib: implement new query parser

mu's query parser is the piece of software that turns your queries
into something the Xapian database can understand. So, if you query
"maildir:/inbox and subject:bla" this must be translated into a
Xapian::Query object which will retrieve the sought after messages.

Since mu's beginning, almost a decade ago, this parser was based on
Xapian's default Xapian::QueryParser. It works okay, but wasn't really
designed for the mu use-case, and had a bit of trouble with anything
that's not A..Z (think: spaces, special characters, unicode etc.).

Over the years, mu added quite a bit of pre-processing trickery to
deal with that. Still, there were corner cases and bugs that were
practically unfixable.

The solution to all of this is to have a custom query processor that
replaces Xapian's, and write it from the ground up to deal with the
special characters etc. I wrote one, as part of my "future, post-1.0
mu" reseach project, and I have now backported it to the mu 0.9.19.

From a technical perspective, this is a major cleanup, and allows us
to get rid of much of the fragile preprocessing both for indexing and
querying. From and end-user perspective this (hopefully) means that
many of the little parsing issues are gone, and it opens the way for
some new features.

From an end-user perspective:
- better support for special characters.
- regexp search! yes, you can now search for regular expressions, e.g.
      subject:/h.ll?o/
  will find subjects with hallo, hello, halo,  philosophy, ...

  As you can imagine, this can be a _heavy_ operation on the database,
  and might take quite a bit longer than a normal query; but it can be
  quite useful.

lib/parser/Makefile.am

@@ -0,0 +1,87 @@
+## Copyright (C) 2017 Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>
+##
+## This program is free software; you can redistribute it and/or modify
+## it under the terms of the GNU General Public License as published by
+## the Free Software Foundation; either version 3 of the License, or
+## (at your option) any later version.
+##
+## This program is distributed in the hope that it will be useful,
+## but WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+## GNU General Public License for more details.
+##
+## You should have received a copy of the GNU General Public License
+## along with this program; if not, write to the Free Software Foundation,
+## Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+
+include $(top_srcdir)/gtest.mk
+
+@VALGRIND_CHECK_RULES@
+
+noinst_PROGRAMS=		\
+	tokenize		\
+	parse
+
+tokenize_SOURCES=		\
+	tokenize.cc
+
+tokenize_LDADD=			\
+	$(GCOV_LDADD)		\
+	libmuxparser.la
+
+parse_SOURCES=			\
+	parse.cc
+
+parse_LDADD=			\
+	$(GCOV_LDADD)		\
+	libmuxparser.la
+
+AM_CXXFLAGS=			\
+	-I$(srcdir)/..		\
+	-I$(top_srcdir)/lib	\
+	$(GLIB_CFLAGS)		\
+	$(XAPIAN_CXXFLAGS)	\
+	$(WARN_CXXFLAGS)	\
+	$(GCOV_CFLAGS)		\
+	-Wno-inline		\
+	-Wno-switch-enum
+
+libmuxparser_la_LIBADD=		\
+	$(WARN_LDFLAGS)		\
+	$(GLIB_LIBS)		\
+	$(XAPIAN_LIBS)		\
+	$(GCOV_LDADD)
+
+noinst_LTLIBRARIES=		\
+	libmuxparser.la
+
+libmuxparser_la_SOURCES=	\
+	data.hh			\
+	parser.cc		\
+	parser.hh		\
+	proc-iface.hh		\
+	tokenizer.cc		\
+	tokenizer.hh		\
+	tree.hh			\
+	utils.cc		\
+	utils.hh		\
+	xapian.cc		\
+	xapian.hh
+
+VALGRIND_SUPPRESSIONS_FILES= ${top_srcdir}/mux.supp
+
+noinst_PROGRAMS+=$(TEST_PROGS)
+
+TEST_PROGS += test-tokenizer
+test_tokenizer_SOURCES=test-tokenizer.cc
+test_tokenizer_LDADD=libmuxparser.la
+
+TEST_PROGS += test-parser
+test_parser_SOURCES=test-parser.cc
+test_parser_LDADD=libmuxparser.la
+
+TEST_PROGS += test-utils
+test_utils_SOURCES=test-utils.cc
+test_utils_LDADD=libmuxparser.la
+
+TESTS=$(TEST_PROGS)