alternating-time-signatures: make proper snippet
Merge branch 'alternating-time-sig' of https://github.com/openlilylib/snippets into alt-ts
Sketch of function with "Gould hyphen"
Added first version of function with integration of "Gould hyphens"
alternating-time-signatures: don't define "last"

The previous commit defined a function "last" - which is a Scheme keyword.
Apart from that it is better not to define such stuff publicly if one can avoid
it. This commit makes the last element of the timesigs available as "lastsig"
in a "let" block.
alternating-time-signatures: reformat gould-irreg
alternating-time-signatures: make hyphen optional WIP

gould-irreg now uses a second boolean? argument.
When that's true hyphens are printed, otherwise not.

TODO: Make that an optional argument.
alternating-time-signatures: make hyphen optional (better)

Now the hyphen is printed when the first element of timesigs is not a list
but #t.

TODO: \alternatingTimeSignatures doesn't work with that yet because it
directly accesses the first element.
alternating-time-signatures: properly handle hyphen

Now hyphens are printed when the first element of the argument list
is exactly #t.
alternating-time-signatures: apply LP-version-switch

Assuming \fractionList will be in LP 2.19.7 this commit implements a switch:
The function is only defined for earlier LP versions, for later versions the
(then) built-in function will be used instead.
alternating-time-signatures: make hyphen condensed

Apply a little bit of negative hspace around the hyphen
in order to make the whole thing slightly narrower
alternating-time-signatures: stub for input validation

The list of time signatures should consist of two-element lists.
When that condition isn't met the function should issue a warning pointing
to the faulty input.

This commit is a a stub and always passes the "check", but the error
handling is already in place
First version of script handling interchangeable metres
Reference to Gould, Behind Bars
alternating-time-signatures: check for malformed input
alternating-time-signatures: make error msg localizable
alternating-time-signatures: clean up a little bit
alternating-time-signatures: Check for malformed input

Now it is nicely contained within one function :-)
alternating-time-signatures: finish documentation
alternating-time-signatures: Add example

Example with floating point timesigs
alternating-time-sigantures: better validity check

Based on David Kastrup's answer to
http://lists.gnu.org/archive/html/lilypond-user/2014-05/msg00324.html