feat(version): introduce version check subcommand

The version subcommand handles pkgver related commands, the first
subcommand being `check`. Check runs nvchecker if a `.nvchecker.toml`
file exists and compares the current pkgver with the latest release.

Introduces nvchecker as optional dependency which has to be installed in
order to use this particular subcommand.

BREAKING CHANGE: formerly pkgctl version would output the version of the
pkgctl tool, now it is used as a version related subcommand.

Fixes #140

Component: pkgctl version
Component: pkgctl version check
Co-authored-by: Christian Heusel <christian@heusel.eu>

3 files changed, 51 insertions, 4 deletions

diff --git a/doc/man/pkgctl-version-check.1.asciidoc b/doc/man/pkgctl-version-check.1.asciidoc
new file mode 100644
index 0000000..97d8c47
--- /dev/null
+++ b/doc/man/pkgctl-version-check.1.asciidoc
@@ -0,0 +1,35 @@
+pkgctl-version-check(1)
+=======================
+
+Name
+----
+pkgctl-version-check - Check if there is an new upstream version available
+
+Synopsis
+--------
+pkgctl version check [OPTIONS] [PKGBASE...]
+
+Description
+-----------
+
+Uses nvchecker, a .nvchecker.toml file and the version specified in the current
+PKGBUILDs pkgver to check if there is a newer package version available to
+which this package could possibly be upgraded.
+
+The current working directory is used if no PKGBASE is specified.
+
+See the section on configuration files in **nvchecker**(1) for possible options
+which can be utilized in .nvchecker.toml.
+
+Options
+-------
+
+*-h, --help*::
+	Show a help text
+
+See Also
+--------
+
+linkman:nvchecker[1]
+
+include::include/footer.asciidoc[]
diff --git a/doc/man/pkgctl-version.1.asciidoc b/doc/man/pkgctl-version.1.asciidoc
index 9beebf5..53a72f3 100644
--- a/doc/man/pkgctl-version.1.asciidoc
+++ b/doc/man/pkgctl-version.1.asciidoc
@@ -3,16 +3,17 @@ pkgctl-version(1)
 
 Name
 ----
-pkgctl-version - Show pkgctl version information
+pkgctl-version - Package version related commands.
+
 
 Synopsis
 --------
-pkgctl version [OPTIONS]
+pkgctl version [OPTIONS] [SUBCOMMAND]
 
 Description
 -----------
 
-Shows the current version information of pkgctl.
+Package version related commands such as checking if a package is out of date.
 
 Options
 -------
@@ -20,4 +21,15 @@ Options
 *-h, --help*::
 	Show a help text
 
+Subcommands
+-----------
+
+pkgctl version check::
+	Check if there is an new upstream version available
+
+See Also
+--------
+
+linkman:pkgctl-version-check[1]
+
 include::include/footer.asciidoc[]
diff --git a/doc/man/pkgctl.1.asciidoc b/doc/man/pkgctl.1.asciidoc
index 24b0613..929ae9a 100644
--- a/doc/man/pkgctl.1.asciidoc
+++ b/doc/man/pkgctl.1.asciidoc
@@ -51,7 +51,7 @@ pkgctl search::
 	Search for an expression across the GitLab packaging group
 
 pkgctl version::
-	Show pkgctl version information
+	Package version related commands
 
 See Also
 --------