Code Merge Request #2: Add read/write flash by partition name (merged)

This patch allows read/write flash by partition name, using following syntax:
rkflashtool r partname >outfile (read flash partition)
rkflashtool w partname <infile (write flash partition)
rkflashtool e partname (erase flash partition)

Changes from v1:

- fix undefined reference to "strnstr" on GNU/Linux
- use soft tabs (4 spaces)