Fix typographical and grammatical errors and inconsistencies.

The initial list of hits was generated with the codespell command
below, and each hit was evaluated and fixed manually while taking
context into consideration.

    DIRS="kernel/ frontends/ backends/ passes/ techlibs/"
    DIRS="${DIRS} libs/ezsat/ libs/subcircuit"
    codespell $DIRS -S *.o -L upto,iff,thru,synopsys,uint

More hits were found by looking through comments and strings manually.

backends/simplec/simplec.cc

@@ -748,7 +748,7 @@ struct SimplecBackend : public Backend {
 		log("\n");
 		log("    write_simplec [options] [filename]\n");
 		log("\n");
-		log("Write simple C code for simulating the design. The C code writen can be used to\n");
+		log("Write simple C code for simulating the design. The C code written can be used to\n");
 		log("simulate the design in a C environment, but the purpose of this command is to\n");
 		log("generate code that works well with C-based formal verification.\n");
 		log("\n");

backends/smt2/smtbmc.py

@@ -87,7 +87,7 @@ yosys-smtbmc [options] <yosys_smt2_output>
 
     --aig <aim_filename>:<aiw_filename>
         like above, but for map files and witness files that do not
-        share a filename prefix (or use differen file extensions).
+        share a filename prefix (or use different file extensions).
 
     --aig-noheader
         the AIGER witness file does not include the status and
@@ -103,8 +103,8 @@ yosys-smtbmc [options] <yosys_smt2_output>
     --presat
         check if the design with assumptions but without assertions
         is SAT before checking if assertions are UNSAT. This will
-        detect if there are contradicting assumtions. In some cases
-        this will also help to "warmup" the solver, potentially
+        detect if there are contradicting assumptions. In some cases
+        this will also help to "warm up" the solver, potentially
         yielding a speedup.
 
     --final-only
@@ -149,7 +149,7 @@ yosys-smtbmc [options] <yosys_smt2_output>
     --append <num_steps>
         add <num_steps> time steps at the end of the trace
         when creating a counter example (this additional time
-        steps will still be constrained by assumtions)
+        steps will still be constrained by assumptions)
 """ + so.helpmsg())
     sys.exit(1)
 

backends/table/table.cc

@@ -109,7 +109,7 @@ struct TableBackend : public Backend {
 				else if (cell->output(conn.first))
 					*f << "out" << "\t";
 				else
-					*f << "unkown" << "\t";
+					*f << "unknown" << "\t";
 
 				*f << log_signal(sigmap(conn.second)) << "\n";
 			}

backends/verilog/verilog_backend.cc

@@ -1447,7 +1447,7 @@ void dump_module(std::ostream &f, std::string indent, RTLIL::Module *module)
 		}
 
 	if (!module->processes.empty())
-		log_warning("Module %s contains unmapped RTLIL proccesses. RTLIL processes\n"
+		log_warning("Module %s contains unmapped RTLIL processes. RTLIL processes\n"
 				"can't always be mapped directly to Verilog always blocks. Unintended\n"
 				"changes in simulation behavior are possible! Use \"proc\" to convert\n"
 				"processes to logic networks and registers.\n", log_id(module));