Allow token weighting

[lewinfox]

Add the ability to supply pre-computed token weights to functions.

levitate::lev_token_set_ratio("ltd bill","ltd b") 
#> 0.625

levitate::lev_ratio("bill","b") 
#> 0.25

levitate::lev_ratio("ltd bill","ltd b") 
#> 0.625

Now, suppose we had lev_ratio( “ltd bill”, “ltd b”, weights = list(ltd = 0.1)). This would construct the lev_ratio as (0.1*3 + 1)/(0.1*3 + 3) = 0.39. Similarly, lev_ratio(“ltd bill”, “ltd b”,weights = list(ltd = 0.01) = 0.34.

Will require:

• Tokenising all input, not just lev_token_*() functions
• Constructing a weight matrix to match the output from stringdist functions
• Matmul weights * scores