add proxy support

[parrasajad]

Examples

socks5:

$ echo AS54115 | asnmap --proxy socks5://127.0.0.1:40932

http:

$ echo AS54115 | asnmap --proxy http://127.0.0.1:8080

input file support:

$ echo AS54115 | asnmap --proxy proxtlist.txt

[Mzack9999]

Please try to refactor the SetProxy method by reducing complexity and increase code readability, for example:

• Move URL checking and setproxy for each item into a proper routine
• Move the file process utility into a subroutine
• Reduce if nesting by preferring err != nil checks and early return

outdated