Add --manifest-path option to all sub-commands

[volks73]

In keeping with the CLI for cargo, there is the --manifest-path <PATH> option to specify the path to a manifest file, Cargo.toml. The default is to use the Cargo.toml file in the current working directory and error if one is not found. This option would allow the user to execute cargo wix commands for a project from outside the current working directory.

Additionally, the <INPUT> argument is currently a path to a manifest file for many of the subcommands. There was a unification effort a while back to make sure the <INPUT> was consistent across all subcommands (#70). This might be a back-track on that effort, but each subcommand appear to need different input. For example, the cargo wix command could use the <INPUT> argument to use multiple WXS files instead of the -I,--include (#92), while the cargo wix sign command could use the <INPUT> argument to be a path to one or more created installers (msi) to sign. The <INPUT> argument name would change to be more descriptive for the specific subcommand. However, every subcommand pretty much needs the Cargo.toml file. This was the reason for using the <INPUT> argument originally. Now with configuration within the Cargo.toml file through package metadata, it might be better to have an explicit option to define a path to a Cargo.toml file instead of trying to make <INPUT> do magic or serve multiple meanings.