Merge pull request #762 from ctheune/ctheune-floats

doc/manual/expressions/builtins.xml

doc/manual/expressions/derivations.xml

doc/manual/expressions/language-values.xml

doc/manual/release-notes/rl-1.11.xml

src/libexpr/eval.cc

src/libexpr/eval.hh

src/libexpr/get-drvs.cc

src/libexpr/get-drvs.hh

src/libexpr/json-to-value.cc

src/libexpr/lexer.l

src/libexpr/nixexpr.cc

src/libexpr/nixexpr.hh

src/libexpr/parser.y

src/libexpr/primops.cc

src/libexpr/value-to-json.cc

src/libexpr/value-to-xml.cc

src/libexpr/value.hh

src/libmain/shared.hh

src/libutil/util.hh

src/nix-env/nix-env.cc