Support top-level comment

[Tsudico]

I am trying to write a header comment that appears before any of my config options. When I try to use a empty path in setComment, it doesn't add the comment at all. It appears that currently I have to prepend the comment to the first entry.

Current use:

config.setComment("version", " Test Configuration\n To reset any value to it's default, remove the value from this file"
    + " The version of the test bench");

Proposed use:

// No path means this is the file's header comment
config.setComment(" Test Configuration\n To reset any value to it's default, remove the value from this file");

// Alternate proposal: use an empty path ""
config.setComment("", " Test Configuration\n To reset any value to it's default, remove the value from this file");

// Normal comment
config.setComment("version", " The version of the test bench");

example.toml

# Test Configuration
# To reset any value to it's default, remove the value from this file

# The version of the test bench
version="1.0.6"

[Debug]
verbose=true
test="complete"