use bison cpp API to support non-trivial types

[lkeegan]

• remove no longer needed YYSTYPE struct
• resolves segfault when parsing long expression #1804

[lkeegan]

It doesn't seem to be slower than the C version, if anything it seems a bit faster for long expressions:

master benchmarks:

First call (initialization)
parse('0') = 0: 13us
Subsequent calls
1us 1us 1us 0us 0us 0us 0us 0us 0us 0us 

Single long benchmark
24ms
(x + y - sin(x)/(-4 + z**2) - x**(y**z))**5001
54ms
(x + y - sin(x)/(-4 + z**2) - x**(y**z))**5001

Repeated short benchmark
15ms
58ms

----------------------------------------------------------------
Benchmark                      Time             CPU   Iterations
----------------------------------------------------------------
parse_0                      723 ns          723 ns       938663
parse_long_expr1/2         10491 ns        10491 ns        66628
parse_long_expr1/8         40238 ns        40238 ns        17423
parse_long_expr1/64       316114 ns       316107 ns         2215
parse_long_expr1/512     2512923 ns      2512878 ns          278
parse_long_expr1/4096   20061868 ns     20061528 ns           35
parse_long_expr1_BigO    4898.08 N       4898.00 N    
parse_long_expr1_RMS           0 %             0 %    
parse_long_expr2/2         12544 ns        12544 ns        55851
parse_long_expr2/8         48027 ns        48026 ns        14578
parse_long_expr2/64       382332 ns       382323 ns         1829
parse_long_expr2/512     3019267 ns      3019182 ns          234
parse_long_expr2/4096   24042647 ns     24042204 ns           29
parse_long_expr2_BigO    5870.23 N       5870.12 N    
parse_long_expr2_RMS           0 %             0 %    

this PR:

First call (initialization)
parse('0') = 0: 12us
Subsequent calls
2us 1us 1us 1us 1us 1us 1us 1us 1us 1us 

Single long benchmark
21ms
(x + y - sin(x)/(-4 + z**2) - x**(y**z))**5001
56ms
(x + y - sin(x)/(-4 + z**2) - x**(y**z))**5001

Repeated short benchmark
14ms
59ms

----------------------------------------------------------------
Benchmark                      Time             CPU   Iterations
----------------------------------------------------------------
parse_0                      737 ns          737 ns       954650
parse_long_expr1/2         10704 ns        10704 ns        65326
parse_long_expr1/8         37873 ns        37871 ns        18530
parse_long_expr1/64       285630 ns       285626 ns         2433
parse_long_expr1/512     2251805 ns      2251708 ns          308
parse_long_expr1/4096   17879598 ns     17879332 ns           39
parse_long_expr1_BigO    4365.67 N       4365.60 N    
parse_long_expr1_RMS           0 %             0 %    
parse_long_expr2/2         12311 ns        12311 ns        56786
parse_long_expr2/8         43450 ns        43449 ns        16036
parse_long_expr2/64       329430 ns       329425 ns         2124
parse_long_expr2/512     2603440 ns      2603424 ns          270
parse_long_expr2/4096   20820959 ns     20820461 ns           34
parse_long_expr2_BigO    5083.28 N       5083.16 N    
parse_long_expr2_RMS           0 %             0 %