Fix state conditions in check_memory and check_swap

[mcktr]

This fixes the state conditions in check_memory and check_swap. This
turns the if/else if/else statements in simple if statements, since they
won't work properly when both thresholds are broken.

This also implements a new function to get a given state as wstring.

Tests

check_memory

.\check_memory.exe -u mb -w 55%
MEMORY WARNING - 13.467% free| 'memory'=551.55MB;2252.5525000000002;;0;4095.55

.\check_memory.exe -u mb -w 55% -c 60%
MEMORY CRITICAL - 10.4848% free| 'memory'=429.41MB;2252.5525000000002;2457.3299999999999;0;4095.55

.\check_memory.exe -u mb -w 80%  -U
MEMORY WARNING - 89.184% used| 'memory'=3652.57MB;3276.4400000000005;;0;4095.55

.\check_memory.exe -u mb -w 80% -c 85% -U
MEMORY CRITICAL - 89.0834% used| 'memory'=3648.46MB;3276.4400000000005;3481.2175000000002;0;4095.55

check_swap

 .\check_swap.exe -u mb -w 90%
SWAP OK 90.0452% free | 'swap'=1990MB;1989;;0;2210

.\check_swap.exe -u mb -w 91%
SWAP WARNING 90.0452% free | 'swap'=1990MB;2011.1000000000001;;0;2210

.\check_swap.exe -u mb -w 91% -c 92%
SWAP CRITICAL 90.0452% free | 'swap'=1990MB;2011.1000000000001;2033.2;0;2210

.\check_swap.exe -u mb -w 8% -U
SWAP WARNING 9.68326% used | 'swap'=214MB;176.80000000000001;;0;2210

.\check_swap.exe -u mb -w 8% -c 9% -U
SWAP CRITICAL 9.68326% used | 'swap'=214MB;176.80000000000001;198.90000000000001;0;2210

fixes #6810