conversion: optimize Scan() scientific scanning

[elee1766]

this pr has the following:

1. the call to strings.SplitN in my original implementation is replaced with Index, and the function is changed to avoid the extra allocation
2. makes the []byte variant properly parse scientific notation.
3. adds pprof debug output to gitignore
4. adds benchmark to bench the scan function

[codecov]

Codecov Report

Merging #127 (0a3cbcb) into master (89e7a3b) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #127   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            5         5           
  Lines         1508      1512    +4     
=========================================
+ Hits          1508      1512    +4