space:fselect and index:fselect fetch data like ordinal select,
but formats the result like mysql does - with columns, column
names etc. fselect converts tuple to strings using json,
extending with spaces and cutting tail if necessary. It is
designed for visual analysis of select result and shouldn't
be used stored procedures.

index:fselect(<key>, <opts>, <fselect_opts>)
space:fselect(<key>, <opts>, <fselect_opts>)

There are some options that can be specified in different ways:
 - among other common options (<opts>) with 'fselect_' prefix.
   (e.g. 'fselect_type=..')
 - in special <fselect_opts> map (with or without prefix).
 - in global variables with 'fselect_' prefix.

The possible options are:
 - type:
    - 'sql' - like mysql result (default).
    - 'gh' (or 'github' or 'markdown') - markdown syntax, for
      copy-pasting to github.
    - 'jira' - jira table syntax (for copy-pasting to jira).
 - widths: array with desired widths of columns.
 - max_width: limit entire length of a row string, longest fields
   will be cut if necessary. Set to 0 (default) to detect and use
   screen width. Set to -1 for no limit.
 - print: (default - false) - print each line instead of adding
   to result.
 - use_nbsp: (default - true) - add invisible spaces to improve
   readability in YAML output. Not applicabble when print=true.

There is also a pair of shortcuts:
index/space:gselect - same as fselect, but with type='gh'.
index/space:jselect - same as fselect, but with type='jira'.

See test/engine/select.test.lua for examples.

Closes #5161