Improve github syntax highlight

Mark shellscripts as awkscripts, as:
- our scripts consist mainly of awk and this change gives better highlight
- it doesn't seem to break highlighter

Author: gizlu

day1/README.md

@@ -1,11 +1,11 @@
 ## task1
 Create sorted list of summaric caloricity of each each elf inventory and extract "the richest elf"
-```sh
+```awk
 awk -vRS="\n\n" -F"\n" '{s=0; for(i=1; i<=NF; ++i) s+=$i; print s}' in.txt | sort | tail -n1
 ```
 
 ## task2
 Create sorted list of summaric caloricity of each each elf inventory and compute sum of "three richest elfs"
-```sh
+```awk
 awk -vRS="\n\n" -F"\n" '{s=0; for(i=1; i<=NF; ++i) s+=$i; print s}' in.txt | sort | tail -n3 | awk '{s+=$1}END{print s}'
 ```

day2/README.md

@@ -1,7 +1,7 @@
 ## task1
 - Convert encoding into more readable notation (R)ock, (P)aper, (S)cisors
 - Create lookup table for score couting and compute score
-```sh
+```awk
 tr 'ABCXYZ' 'RPSRPS' < in.txt |
 awk 'BEGIN {
 LUT["RR"]=4; LUT["PP"]=5; LUT["SS"]=6; # draws
@@ -13,7 +13,7 @@ END { print points }'
 ## task2
 - Convert encoding into more readable notation (R)ock, (P)aper, (S)cisors, (L)ose, (D)raw, (W)in
 - Create lookup table for score couting and compute score
-```sh
+```awk
 tr 'ABCXYZ' 'RPSLDW' < in.txt |
 awk 'BEGIN {
 LUT["RD"]=4; LUT["PD"]=5; LUT["SD"]=6; # draws

day3/README.md

@@ -2,7 +2,7 @@
 - build lookup table for priorities
 - for each line find item present in both compartments and add its piority to sum
 
-```sh
+```awk
 awk -F '' '
 BEGIN{ for(i=0; i<26;i++) LUT[sprintf("%c",i+97)]=i+1; } # a-z (97 - "a" ascii code)
 BEGIN{ for(i=0; i<26;i++) LUT[sprintf("%c",i+65)]=i+27; } # A-Z (65 - "A" ascii code)
@@ -15,7 +15,7 @@ BEGIN{ for(i=0; i<26;i++) LUT[sprintf("%c",i+65)]=i+27; } # A-Z (65 - "A" ascii
 - join every group of 3 lines into one line
 - build lookup table for priorities
 - for each group find item present in all 3 rucksacks and add its piority to sum
-```sh
+```awk
 xargs -n3 <in.txt | awk '
 BEGIN{ for(i=0; i<26;i++) LUT[sprintf("%c",i+97)]=i+1; } # a-z (97 - "a" ascii code)
 BEGIN{ for(i=0; i<26;i++) LUT[sprintf("%c",i+65)]=i+27; } # A-Z (65 - "A" ascii code)