ulimit: add new limits from Linux

Short options are taken from prlimit(1) where appropriate.

Closes #8786.

doc_src/cmds/ulimit.rst

@@ -24,9 +24,15 @@ Use one of the following switches to specify which resource limit to set or repo
 **-d** or **--data-size**
     The maximum size of a process' data segment.
 
+**-e** or **--nice**
+    Controls the maximum nice value; on Linux, this value is subtracted from 20 to give the effective value.
+
 **-f** or **--file-size**
     The maximum size of files created by a process.
 
+**-i** or **--pending-signals**
+    The maximum number of signals that may be queued.
+
 **-l** or **--lock-size**
     The maximum size that may be locked into memory.
 
@@ -36,6 +42,12 @@ Use one of the following switches to specify which resource limit to set or repo
 **-n** or **--file-descriptor-count**
     The maximum number of open file descriptors.
 
+**-q** or **--queue-size**
+    The maximum size of data in POSIX message queues.
+
+**-r** or **--realtime-priority**
+    The maximum realtime scheduling priority.
+
 **-s** or **--stack-size**
     The maximum stack size.
 
@@ -48,6 +60,9 @@ Use one of the following switches to specify which resource limit to set or repo
 **-v** or **--virtual-memory-size**
     The maximum amount of virtual memory available to the shell.
 
+**-y** or **--realtime-maxtime**
+    The maximum contiguous realtime CPU time in microseconds.
+
 Note that not all these limits are available in all operating systems.
 
 The value of limit can be a number in the unit specified for the resource or one of the special values ``hard``, ``soft``, or ``unlimited``, which stand for the current hard limit, the current soft limit, and no limit, respectively.