OPENFAAS_TEMPLATE_URL override and other minor fixes
Changelog:
- Override for template pull URL via ENV variable OPENFAAS_TEMPLATE_URL #515 by s8sg
- Adds support for additional HTTP verbs PATCH, OPTIONS and HEAD #505 by ewilde
- Fixes issue with faas-cli build for same folder #480 by viveksyngh
- Configurable handler directory #504 by dmcclory
- Proxy version command HTTP call #520 by viveksyngh