Support proxying SSL connections
Only support proxied SSL with Python >= 2.7
Unbreak Config on empty options

This prevents the following issue:

Traceback (most recent call last):
  File "/usr/local/bin/s3cmd", line 2521, in <module>
    rc = main()
  File "/usr/local/bin/s3cmd", line 2261, in main
    cfg = Config(options.config, options.access_key, options.secret_key)
  File "/usr/local/lib/python2.7/dist-packages/S3/Config.py", line 126, in __init__
    self.read_config_file(configfile)
  File "/usr/local/lib/python2.7/dist-packages/S3/Config.py", line 226, in read_config_file
    self.update_option(option, cp.get(option).strip())
AttributeError: 'NoneType' object has no attribute 'strip'
rewrite of README into markdown
Backported changes from the following pull request: https://github.com/s3tools/s3cmd/pull/369 regarding aws pricing.
Updated README.md with latest changes of S3 prices:
https://aws.amazon.com/fr/blogs/aws/aws-data-transfer-price-reduction/?sc_ichannel=EM&sc_icountry=global&sc_icampaigntype=launch&sc_icampaign=EM_128506540&sc_idetail=em_1778261631&ref_=pe_411040_128506540_12