libsmartcols: (filter) add ability to cast data

libsmartcols: (filter) add ability to cast data

* add FLOAT type for JSON

  JSON standard does not care and everything is number, but for libsmartcols
  it would be better to differentiate between the types.

* add functions to cast data in the filter param

* cast data from scols rows

* cast data in the filter expression if necessary

Signed-off-by: Karel Zak <kzak@redhat.com>