Add union ("expr1 | expr2") support
tabs to spaces. Sorry)
some random refactorings. Union duplication filter. 'contains()' xpath function added
Add support for variable args count for xpath functions. Add concat() function.
README updated (markdown + XPath 1.0 coverage lists)
Partially implemented arithmetic operations in predicates
no tabs again
Full arithmetic operations support
Add dummy axes handlers
Add universal test_node/3 ("[7] NodeTest" from spec) and apply it for some axes
Remove unused clause of execute/2
Better axes support
  * Add node_test to "self", "descendant-or-self", "attribute" axes
  * Add "descendant" axis
  * Add support for "processing-instruction(Name)"
  * Add "string_value" for attributes
add NodeTest support to "parent" axis
Add NodeTest to following-sibling and preceeding-sibling
Add test for incorrect descendant(-or-self) + text() behaviour
comments and workaround for descendant+text() bug
Minor fix
not() function implemented
Add some typespecs
Fix "negative" handling (like "-1", "-count(node)" etc)