Contributes to:
Issue #218, https://github.com/espeak-ng/espeak-ng/issues/218

Changes:
language files have a new keyword letterVowel. It can be a latin alphabet from a-z or a hex value (used by bulgarian).
Errors in parsing the values are only reported, nothing is done about them.

About testing:
I haven't noticed any differences in the output audio with letterVowel set or unset in any tested language. The code seems to work and the correct bits seem to be set, but I don't know how to confirm from the final audio.

TODO:
1. Write better documentation in docs/voices.md
2. The code uses new_translator. Should it use translator instead?

See issue #8, https://github.com/espeak-ng/espeak-ng/issues/8

There might still be some ints that could be changed to boolean.

Possible regressions in fifo.c:
int fifo_is_busy() and int fifo_is_command_enabled() used to return an int. Now they return a boolean. This might cause problems on systems where stdbool true/false is something else than 1/0.

This reverts commit 119c200e00.

This replaces uses of:

	memcpy(dst, src, strlen(src))

with:

	strcpy(dst, src)

This fixes issues with reading past the end of the copied buffer
(e.g. when processing word-based replacements for emoji characters)
by ensuring that the destination buffer is null terminated.

Reported by Michael Curran <[email protected]>

Clang static analysis reports this as 'Assigned value is garbage
or undefined'.

Clang static analysis reports these as 'Result of operation is
garbage or undefined' errors.

Clang static analysis reports an 'Assigned value is garbage or
undefined' for this. If no points were read from the file, the
`n_points` variable is 0 and `env_x[n_points-1]` performs an
out-of-bounds access.

Clang static analysis reports an 'Assigned value is garbage or
undefined' error. This happens if the default_tune data has not
been copied in the kTUNE case.

Extending this further, it does not make sense to save the tune
data if the tune was not found, or if the tune already exists.

This was identified by the clang static analyser. The letter
variable is set in the various match_type switch cases, so
does not need to be initialised in the start of the while loop.