fix: require that c32 addresses start with S

[jcnelson]

Right now, c32addressDecode() will decode the address bP2CT665Q0JB7P39TZ7BST0QYCAQSMJWBZK8QT35J. Given that clients of this library are expecting that this method not decode invalid Stacks addresses, this method should be fixed to require that the leading character is S. This PR addresses this. Context: stacks-network/stacks-utils#21

[codecov]

Codecov Report

Merging #14 (5a9d37b) into master (5b0e305) will increase coverage by 0.08%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #14      +/-   ##
==========================================
+ Coverage   91.62%   91.70%   +0.08%     
==========================================
  Files           5        5              
  Lines         191      193       +2     
  Branches       32       33       +1     
==========================================
+ Hits          175      177       +2     
  Misses          5        5              
  Partials       11       11              

Impacted Files	Coverage Δ
src/address.ts	95.74% <100.00%> (+0.18%)	⬆️

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[aulneau]

@jcnelson thanks for this. I'm curious if there is a better solution than requiring that the string start with S? Or are there any number of c32 addresses and they are all "valid" regardless of what it starts with?

[jcnelson]

So, way back in the day (Stacks 1.0), it was decided that the first letter of the address should simply be S for branding purposes. It's entirely cosmetic. But, the code never required this -- if you mistyped the first letter, you'd still have the same address (because the hash160 is encoded in the letters following the S). However, upstream clients aren't expecting this.

[jcnelson]

Soooo.....can I merge this?