Update prometheus client version

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <[email protected]>

Fix golang version during build flow

**What**
- Fix copy-pasta error and use Go 1.15 for both the build and publish
  workflows

Signed-off-by: Lucas Roesler <[email protected]>

Update Go version to 1.15

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <[email protected]>

Switch to go modules

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <[email protected]>

Update README

Clarify aims and status of the component within the project.

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <[email protected]>

forward original request's context

Signed-off-by: Hilário Coelho <[email protected]>

Allow Int values and parse as Seconds for Durations

The timeout values could be accidentally set as ints by a user
rather than golang durations. This meant that "5" gets parsed
to 5ms not 5s. Now we try and parse non duration strings as
seconds.

This has been tested by creating a function with the old binary,
setting the timeouts for read, write and exec to "5" and 5.
These are interpreted as 0s.

New binary swapped in and re-deployed, this then worked as our
waits were less than the 5 seconds, when expanded over 5s (the waits)
then the fn was stopped

Signed-off-by: Alistair Hey <[email protected]>

Add Http_Transfer_Encoding

This affects serializing and streaming modes and lets the caller
know what the encoding mode is when that is set. For instance if
the value is "chunked", the Http_Content_Length must be ignored.

Closes: #89

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <[email protected]>

Update of-watchdog to use Go 1.13

Go 1.13 will be used for the distribution version of the watchdog.

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <[email protected]>

Fix feedback from #87

This commit applies the feedback given in #87 and uses a flag
to both add documentation and to match the style of the rest
of the project.

This change is only useful for exec healthchecks and not for
http probes. Wherever possible users should only use http
healthchecks since exec is very resource intensive.

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <[email protected]>