Feat/tx fees

[theflyingcodr]

This refactors the fee calculations to improve accuracy and also provide a breakdown of the fees paid and the breakdown of the tx bytes.

This also includes some improvements to change calcs, change will now not be added if it will be below the dust limit after covering outputs and tx fees.

New methods added to the tx:

 isEnough, err := tx.IsFeePaidEnough(feeQuote) // are current fees being paid by tx enough to meet given feeQuote?
 txFees, err := tx.EstimateFeesPaid(feeQuote) // fees required to be paid by tx
 size := tx.Size() / / current tx size (int) with nothing added
 txSize := tx.SizeWithTypes() / / current tx size (including types) with nothing added
 size, err := tx.EstimateSize() // add 107 bytes for any unsigned inputs
 txSize, err := tx.EstimateSizeWithTypes() // add 107 bytes for any unsigned inputs (including types)

[codecov-commenter]

Codecov Report

Merging #42 (bd71290) into master (b8ebe83) will decrease coverage by 0.20%.
The diff coverage is 73.75%.

@@            Coverage Diff             @@
##           master      #42      +/-   ##
==========================================
- Coverage   86.31%   86.10%   -0.21%     
==========================================
  Files          26       26              
  Lines        2762     2800      +38     
==========================================
+ Hits         2384     2411      +27     
- Misses        260      268       +8     
- Partials      118      121       +3     

Impacted Files	Coverage Δ
tx.go	79.67% <68.51%> (-4.54%)	⬇️
txchange.go	82.75% <84.61%> (+4.38%)	⬆️

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